内容表

  • 内置类型
    • 真值测试
    • 布尔运算 — and , or , not
    • 比较
    • 数值类型 — int , float , complex
      • 整数类型的按位运算
      • 额外整数类型方法
      • 额外浮点方法
      • 数值类型的哈希
    • Boolean Type - bool
    • 迭代器类型
      • 生成器类型
    • 序列类型 — list , tuple , range
      • 常见序列操作
      • 不可变序列类型
      • 可变序列类型
      • 列表
      • 元组
      • 范围
    • 文本序列类型 — str
      • 字符串方法
      • printf 样式字符串格式化
    • 二进制序列类型 — bytes , bytearray , memoryview
      • bytes 对象
      • bytearray 对象
      • bytes 和 bytearray 操作
      • printf 样式字节格式化
      • 内存视图
    • 集类型 — set , frozenset
    • 映射类型 — dict
      • 字典视图对象
    • 上下文管理器类型
    • 类型注解类型 — 一般别名 , Union
      • 一般别名类型
        • 标准泛型类
        • 特殊属性对于 GenericAlias 对象
      • Union 类型
    • 其它内置类型
      • 模块
      • 类和类实例
      • 函数
      • 方法
      • 代码对象
      • 类型对象
      • Null 对象
      • 省略对象
      • 未实现对象
      • 内部对象
    • 特殊属性
    • 整数字符串转换长度局限性
      • 受影响 API
      • 配置限制
      • 推荐配置
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    2. Python 3.12.4
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    8. 内置类型

    内置类型 ¶

    以下章节描述解释器内置的标准类型。

    主要内置类型，包括：数值、序列、映射、类、实例及异常。

    某些集合类是可变的。添加、减去或原位重新排列其成员且不返回特定项的方法，从不返回集合实例本身而是 None .

    某些操作支持几种对象类型；尤其，实际上所有对象都可以进行相等比较、测试真值及转换为字符串 (采用 repr() 函数或稍微不同的 str() 函数)。隐式使用后一函数当对象写入通过 print() 函数。

    真值测试 ¶

    可以测试任何对象的真值，对于用于 if or while 条件或作为以下布尔运算的操作数。

    默认情况下，对象被认为是 True ，除非其类定义的 __bool__() 方法返回 False 或 __len__() 方法返回 0，当调用对象时。 [ 1 ] 这里是被认为是 False 的大多数内置对象：

    • 定义为 False 的常量： None and False

    • 任何数值类型的零： 0 , 0.0 , 0j , Decimal(0) , Fraction(0, 1)

    • 空序列和集合： '' , () , [] , {} , set() , range(0)

    拥有 Boolean (布尔) 结果的运算和内置函数始终返回 0 or False 对于 false 和 1 or True 对于 true，除非另有说明 (重要例外：布尔运算 or and and 始终返回它们的操作数之一)。

    布尔运算 — and , or , not ¶

    这些是布尔运算，按优先级升序排序：

    操作

    结果

    注意事项

    x or y

    if x 为 true，则 x ，否则 y

    		(1)

    x and y

    if x 为 False，那么 x ，否则 y

    		(2)

    not x

    if x 为 False，那么 True ，否则 False

    		(3)

    注意事项：

    1. 这是短路运算符，所以它只评估第 2 自变量，若第 1 自变量为 False。

    2. 这是短路运算符，所以它只评估第 2 自变量，若第 1 自变量为 True。

    3. not 拥有比非布尔运算符更低的优先级，所以 not a == b 被解释成 not (a == b) ，和 a == not b 是句法错误。

    比较 ¶

    Python 中存在 8 种比较操作。它们拥有相同优先级 (高于布尔运算)。比较可以任意连锁；例如， x < y <= z 相当于 x < y and y <= z ，除了 y 只评估 1 次 (但在 2 种情况下， z 根本不评估当 x < y 被发现为 False)。

    此表汇总了比较操作：

    操作

    含义

    <

    		严格小于

    <=

    		小于等于

    >

    		严格大于

    >=

    		大于等于

    ==

    		equal

    !=

    		不等于

    is

    		对象身份

    is not

    		否定对象身份

    Objects of different types, except different numeric types, never compare equal. The == operator is always defined but for some object types (for example, class objects) is equivalent to is 。 < , <= , > and >= operators are only defined where they make sense; for example, they raise a TypeError exception when one of the arguments is a complex number.

    Non-identical instances of a class normally compare as non-equal unless the class defines the __eq__() 方法。

    Instances of a class cannot be ordered with respect to other instances of the same class, or other types of object, unless the class defines enough of the methods __lt__() , __le__() , __gt__() ，和 __ge__() (一般而言， __lt__() and __eq__() are sufficient, if you want the conventional meanings of the comparison operators).

    行为对于 is and is not 操作符无法定制；还可以将它们应用于任何 2 对象，且从不引发异常。

    另外，具有相同句法优先级的 2 操作 in and not in ，的支持是通过类型 iterable 或实现 __contains__() 方法。

    数值类型 — int , float , complex ¶

    有 3 种截然不同的数值类型： integers , 浮点数 ，和 复数 . In addition, Booleans are a subtype of integers. Integers have unlimited precision. Floating point numbers are usually implemented using double in C; information about the precision and internal representation of floating point numbers for the machine on which your program is running is available in sys.float_info . Complex numbers have a real and imaginary part, which are each a floating point number. To extract these parts from a complex number z ，使用 z.real and z.imag . (The standard library includes the additional numeric types fractions.Fraction , for rationals, and decimal.Decimal , for floating-point numbers with user-definable precision.)

    Numbers are created by numeric literals or as the result of built-in functions and operators. Unadorned integer literals (including hex, octal and binary numbers) yield integers. Numeric literals containing a decimal point or an exponent sign yield floating point numbers. Appending 'j' or 'J' to a numeric literal yields an imaginary number (a complex number with a zero real part) which you can add to an integer or float to get a complex number with real and imaginary parts.

    Python fully supports mixed arithmetic: when a binary arithmetic operator has operands of different numeric types, the operand with the “narrower” type is widened to that of the other, where integer is narrower than floating point, which is narrower than complex. A comparison between numbers of different types behaves as though the exact values of those numbers were being compared. [ 2 ]

    构造函数 int() , float() ，和 complex() 可用于产生特定类型的数字。

    All numeric types (except complex) support the following operations (for priorities of the operations, see 运算符优先级 ):

    操作

    结果

    注意事项

    完整文档编制

    x + y

    和对于 x and y

    x - y

    difference of x and y

    x * y

    乘积对于 x and y

    x / y

    quotient of x and y

    x // y

    floored quotient of x and y

    		(1)(2)

    x % y

    余数对于 x / y

    		(2)

    -x

    x negated

    +x

    x unchanged

    abs(x)

    absolute value or magnitude of x

    abs()

    int(x)

    x 被转换成整数

    		(3)(6)

    int()

    float(x)

    x 被转换成浮点数

    		(4)(6)

    float()

    complex(re, im)

    a complex number with real part re , imaginary part im . im defaults to zero.

    		(6)

    complex()

    c.conjugate()

    conjugate of the complex number c

    divmod(x, y)

    对 (x // y, x % y)

    		(2)

    divmod()

    pow(x, y)

    x 到幂 y

    		(5)

    pow()

    x ** y

    x 到幂 y

    		(5)

    注意事项：

    1. Also referred to as integer division. For operands of type int , the result has type int . For operands of type float , the result has type float . In general, the result is a whole integer, though the result’s type is not necessarily int . The result is always rounded towards minus infinity: 1//2 is 0 , (-1)//2 is -1 , 1//(-2) is -1 ，和 (-1)//(-2) is 0 .

    2. 不适用于复数。相反，转换为浮点数使用 abs() 若合适。

    3. Conversion from float to int truncates, discarding the fractional part. See functions math.floor() and math.ceil() for alternative conversions.

    4. float also accepts the strings “nan” and “inf” with an optional prefix “+” or “-” for Not a Number (NaN) and positive or negative infinity.

    5. Python 定义 pow(0, 0) and 0 ** 0 到 1 , as is common for programming languages.

    6. The numeric literals accepted include the digits 0 to 9 or any Unicode equivalent (code points with the Nd 特性)。

      见 the Unicode Standard for a complete list of code points with the Nd 特性。

    所有 numbers.Real 类型 ( int and float ) 还包括以下操作：

    操作

    结果

    math.trunc(x)

    x truncated to Integral

    round(x[, n])

    x 四舍五入到 n digits, rounding half to even. If n is omitted, it defaults to 0.

    math.floor(x)

    the greatest Integral <= x

    math.ceil(x)

    the least Integral >= x

    其它数值运算，见 math and cmath 模块。

    整数类型的按位运算 ¶

    Bitwise operations only make sense for integers. The result of bitwise operations is calculated as though carried out in two’s complement with an infinite number of sign bits.

    The priorities of the binary bitwise operations are all lower than the numeric operations and higher than the comparisons; the unary operation ~ 具有相同优先级，如同其它一元数值运算 ( + and - ).

    此表按优先级升序排序，列出按位运算：

    操作

    结果

    注意事项

    x | y

    bitwise or of x and y

    		(4)

    x ^ y

    bitwise exclusive or of x and y

    		(4)

    x & y

    bitwise and of x and y

    		(4)

    x << n

    x shifted left by n bits

    		(1)(2)

    x >> n

    x shifted right by n bits

    		(1)(3)

    ~x

    the bits of x inverted

    注意事项：

    1. 负移位计数是非法的，并会导致 ValueError 要被引发。

    2. 向左移位 n 位，相当于乘以 pow(2, n) .

    3. 向右移位 n bits is equivalent to floor division by pow(2, n) .

    4. 履行这些计算，采用至少一额外符号扩展位表示有限的 2 的补码 (工作位宽 1 + max(x.bit_length(), y.bit_length()) 或更多) 足以获取与无穷多符号位相同的结果。

    额外整数类型方法 ¶

    int 类型实现 numbers.Integral 抽象基类 。此外，它还提供一些其它方法：

    int. bit_length ( ) ¶

    Return the number of bits necessary to represent an integer in binary, excluding the sign and leading zeros: 

    >>> n = -37
>>> bin(n)
'-0b100101'
>>> n.bit_length()
6

    更准确地说，若 x 非 0，那么 x.bit_length() 是唯一正整数 k 这样 2**(k-1) <= abs(x) < 2**k . Equivalently, when abs(x) is small enough to have a correctly rounded logarithm, then k = 1 + int(log(abs(x), 2)) 。若 x is zero, then x.bit_length() 返回 0 .

    等效于： 

    def bit_length(self):
    s = bin(self)       # binary representation:  bin(-37) --> '-0b100101'
    s = s.lstrip('-0b') # remove leading zeros and minus sign
    return len(s)       # len('100101') --> 6

    Added in version 3.1.

    int. bit_count ( ) ¶

    Return the number of ones in the binary representation of the absolute value of the integer. This is also known as the population count. Example: 

    >>> n = 19
>>> bin(n)
'0b10011'
>>> n.bit_count()
3
>>> (-n).bit_count()
3

    等效于： 

    def bit_count(self):
    return bin(self).count("1")

    Added in version 3.10.

    int. to_bytes ( length = 1 , byteorder = 'big' , * , signed = False ) ¶

    返回表示整数的字节数组。 

    >>> (1024).to_bytes(2, byteorder='big')
b'\x04\x00'
>>> (1024).to_bytes(10, byteorder='big')
b'\x00\x00\x00\x00\x00\x00\x00\x00\x04\x00'
>>> (-1024).to_bytes(10, byteorder='big', signed=True)
b'\xff\xff\xff\xff\xff\xff\xff\xff\xfc\x00'
>>> x = 1000
>>> x.to_bytes((x.bit_length() + 7) // 8, byteorder='little')
b'\xe8\x03'

    整数的表示使用 length bytes, and defaults to 1. An OverflowError 被引发若整数不能按给定字节数表示。

    The byteorder argument determines the byte order used to represent the integer, and defaults to "big" 。若 byteorder is "big" , the most significant byte is at the beginning of the byte array. If byteorder is "little" , the most significant byte is at the end of the byte array.

    The signed 自变量确定是否使用 2 的补码表示整数。若 signed is False and a negative integer is given, an OverflowError is raised. The default value for signed is False .

    The default values can be used to conveniently turn an integer into a single byte object: 

    >>> (65).to_bytes()
b'A'

    However, when using the default arguments, don’t try to convert a value greater than 255 or you’ll get an OverflowError .

    等效于： 

    def to_bytes(n, length=1, byteorder='big', signed=False):
    if byteorder == 'little':
        order = range(length)
    elif byteorder == 'big':
        order = reversed(range(length))
    else:
        raise ValueError("byteorder must be either 'little' or 'big'")
    return bytes((n >> i*8) & 0xff for i in order)

    Added in version 3.2.

    3.11 版改变： Added default argument values for length and byteorder .

    classmethod int. from_bytes ( bytes , byteorder = 'big' , * , signed = False ) ¶

    Return the integer represented by the given array of bytes. 

    >>> int.from_bytes(b'\x00\x10', byteorder='big')
16
>>> int.from_bytes(b'\x00\x10', byteorder='little')
4096
>>> int.from_bytes(b'\xfc\x00', byteorder='big', signed=True)
-1024
>>> int.from_bytes(b'\xfc\x00', byteorder='big', signed=False)
64512
>>> int.from_bytes([255, 0, 0], byteorder='big')
16711680

    自变量 bytes 必须是 像字节对象 或产生 bytes 的可迭代。

    The byteorder argument determines the byte order used to represent the integer, and defaults to "big" 。若 byteorder is "big" , the most significant byte is at the beginning of the byte array. If byteorder is "little" , the most significant byte is at the end of the byte array. To request the native byte order of the host system, use sys.byteorder as the byte order value.

    The signed argument indicates whether two’s complement is used to represent the integer.

    等效于： 

    def from_bytes(bytes, byteorder='big', signed=False):
    if byteorder == 'little':
        little_ordered = list(bytes)
    elif byteorder == 'big':
        little_ordered = list(reversed(bytes))
    else:
        raise ValueError("byteorder must be either 'little' or 'big'")
    n = sum(b << i*8 for i, b in enumerate(little_ordered))
    if signed and little_ordered and (little_ordered[-1] & 0x80):
        n -= 1 << 8*len(little_ordered)
    return n

    Added in version 3.2.

    3.11 版改变： Added default argument value for byteorder .

    int. as_integer_ratio ( ) ¶

    Return a pair of integers whose ratio is equal to the original integer and has a positive denominator. The integer ratio of integers (whole numbers) is always the integer as the numerator and 1 as the denominator.

    Added in version 3.8.

    int. is_integer ( ) ¶

    返回 True . Exists for duck type compatibility with float.is_integer() .

    3.12 版添加。

    额外浮点方法 ¶

    浮点类型实现 numbers.Real 抽象基类 . float also has the following additional methods.

    float. as_integer_ratio ( ) ¶

    Return a pair of integers whose ratio is exactly equal to the original float. The ratio is in lowest terms and has a positive denominator. Raises OverflowError on infinities and a ValueError on NaNs.

    float. is_integer ( ) ¶

    返回 True if the float instance is finite with integral value, and False 否则： 

    >>> (-2.0).is_integer()
True
>>> (3.2).is_integer()
False

    Two methods support conversion to and from hexadecimal strings. Since Python’s floats are stored internally as binary numbers, converting a float to or from a decimal string usually involves a small rounding error. In contrast, hexadecimal strings allow exact representation and specification of floating-point numbers. This can be useful when debugging, and in numerical work.

    float. hex ( ) ¶

    Return a representation of a floating-point number as a hexadecimal string. For finite floating-point numbers, this representation will always include a leading 0x and a trailing p and exponent.

    classmethod float. fromhex ( s ) ¶

    Class method to return the float represented by a hexadecimal string s . The string s may have leading and trailing whitespace.

    注意， float.hex() 是实例方法，而 float.fromhex() 是类方法。

    A hexadecimal string takes the form: 

    [sign] ['0x'] integer ['.' fraction] ['p' exponent]

    其中可选 sign may by either + or - , integer and fraction are strings of hexadecimal digits, and exponent is a decimal integer with an optional leading sign. Case is not significant, and there must be at least one hexadecimal digit in either the integer or the fraction. This syntax is similar to the syntax specified in section 6.4.4.2 of the C99 standard, and also to the syntax used in Java 1.5 onwards. In particular, the output of float.hex() is usable as a hexadecimal floating-point literal in C or Java code, and hexadecimal strings produced by C’s %a format character or Java’s Double.toHexString are accepted by float.fromhex() .

    Note that the exponent is written in decimal rather than hexadecimal, and that it gives the power of 2 by which to multiply the coefficient. For example, the hexadecimal string 0x3.a7p10 represents the floating-point number (3 + 10./16 + 7./16**2) * 2.0**10 ，或 3740.0 : 

    >>> float.fromhex('0x3.a7p10')
3740.0

    Applying the reverse conversion to 3740.0 gives a different hexadecimal string representing the same number: 

    >>> float.hex(3740.0)
'0x1.d380000000000p+11'

    数值类型的哈希 ¶

    For numbers x and y , possibly of different types, it’s a requirement that hash(x) == hash(y) whenever x == y (见 __hash__() method documentation for more details). For ease of implementation and efficiency across a variety of numeric types (including int , float , decimal.Decimal and fractions.Fraction ) Python’s hash for numeric types is based on a single mathematical function that’s defined for any rational number, and hence applies to all instances of int and fractions.Fraction , and all finite instances of float and decimal.Decimal . Essentially, this function is given by reduction modulo P for a fixed prime P . The value of P is made available to Python as the modulus attribute of sys.hash_info .

    CPython 实现细节： 目前，使用的素数是 P = 2**31 - 1 on machines with 32-bit C longs and P = 2**61 - 1 on machines with 64-bit C longs.

    这里是详细规则：

    • 若 x = m / n is a nonnegative rational number and n is not divisible by P , define hash(x) as m * invmod(n, P) % P ，其中 invmod(n, P) gives the inverse of n 模 P .

    • 若 x = m / n is a nonnegative rational number and n is divisible by P (但 m is not) then n has no inverse modulo P and the rule above doesn’t apply; in this case define hash(x) to be the constant value sys.hash_info.inf .

    • 若 x = m / n is a negative rational number define hash(x) as -hash(-x) 。若结果哈希为 -1 ，替换它采用 -2 .

    • The particular values sys.hash_info.inf and -sys.hash_info.inf are used as hash values for positive infinity or negative infinity (respectively).

    • 对于 complex 编号 z , the hash values of the real and imaginary parts are combined by computing hash(z.real) + sys.hash_info.imag * hash(z.imag) , reduced modulo 2**sys.hash_info.width so that it lies in range(-2**(sys.hash_info.width - 1), 2**(sys.hash_info.width - 1)) . Again, if the result is -1 , it’s replaced with -2 .

    To clarify the above rules, here’s some example Python code, equivalent to the built-in hash, for computing the hash of a rational number, float ，或 complex : 

    import sys, math
def hash_fraction(m, n):
    """Compute the hash of a rational number m / n.
    Assumes m and n are integers, with n positive.
    Equivalent to hash(fractions.Fraction(m, n)).
    """
    P = sys.hash_info.modulus
    # Remove common factors of P.  (Unnecessary if m and n already coprime.)
    while m % P == n % P == 0:
        m, n = m // P, n // P
    if n % P == 0:
        hash_value = sys.hash_info.inf
    else:
        # Fermat's Little Theorem: pow(n, P-1, P) is 1, so
        # pow(n, P-2, P) gives the inverse of n modulo P.
        hash_value = (abs(m) % P) * pow(n, P - 2, P) % P
    if m < 0:
        hash_value = -hash_value
    if hash_value == -1:
        hash_value = -2
    return hash_value
def hash_float(x):
    """Compute the hash of a float x."""
    if math.isnan(x):
        return object.__hash__(x)
    elif math.isinf(x):
        return sys.hash_info.inf if x > 0 else -sys.hash_info.inf
    else:
        return hash_fraction(*x.as_integer_ratio())
def hash_complex(z):
    """Compute the hash of a complex number z."""
    hash_value = hash_float(z.real) + sys.hash_info.imag * hash_float(z.imag)
    # do a signed reduction modulo 2**sys.hash_info.width
    M = 2**(sys.hash_info.width - 1)
    hash_value = (hash_value & (M - 1)) - (hash_value & M)
    if hash_value == -1:
        hash_value = -2
    return hash_value

    Boolean Type - bool ¶

    Booleans represent truth values. The bool type has exactly two constant instances: True and False .

    内置函数 bool() converts any value to a boolean, if the value can be interpreted as a truth value (see section 真值测试 above).

    For logical operations, use the boolean operators and , or and not . When applying the bitwise operators & , | , ^ to two booleans, they return a bool equivalent to the logical operations “and”, “or”, “xor”. However, the logical operators and , or and != should be preferred over & , | and ^ .

    Deprecated since version 3.12: The use of the bitwise inversion operator ~ is deprecated and will raise an error in Python 3.14.

    bool 是子类化的 int (见 数值类型 — 整数、浮点数、复数 ). In many numeric contexts, False and True behave like the integers 0 and 1, respectively. However, relying on this is discouraged; explicitly convert using int() 代替。

    迭代器类型 ¶

    Python supports a concept of iteration over containers. This is implemented using two distinct methods; these are used to allow user-defined classes to support iteration. Sequences, described below in more detail, always support the iteration methods.

    One method needs to be defined for container objects to provide iterable support:

    container. __iter__ ( ) ¶

    返回 iterator object. The object is required to support the iterator protocol described below. If a container supports different types of iteration, additional methods can be provided to specifically request iterators for those iteration types. (An example of an object supporting multiple forms of iteration would be a tree structure which supports both breadth-first and depth-first traversal.) This method corresponds to the tp_iter slot of the type structure for Python objects in the Python/C API.

    The iterator objects themselves are required to support the following two methods, which together form the 迭代器协议 :

    iterator. __iter__ ( ) ¶

    返回 iterator object itself. This is required to allow both containers and iterators to be used with the for and in statements. This method corresponds to the tp_iter slot of the type structure for Python objects in the Python/C API.

    iterator. __next__ ( ) ¶

    Return the next item from the iterator . If there are no further items, raise the StopIteration exception. This method corresponds to the tp_iternext slot of the type structure for Python objects in the Python/C API.

    Python defines several iterator objects to support iteration over general and specific sequence types, dictionaries, and other more specialized forms. The specific types are not important beyond their implementation of the iterator protocol.

    一旦迭代器的 __next__() 方法引发 StopIteration , it must continue to do so on subsequent calls. Implementations that do not obey this property are deemed broken.

    生成器类型 ¶

    Python 的 generator s provide a convenient way to implement the iterator protocol. If a container object’s __iter__() method is implemented as a generator, it will automatically return an iterator object (technically, a generator object) supplying the __iter__() and __next__() methods. More information about generators can be found in the documentation for the yield expression .

    序列类型 — list , tuple , range ¶

    There are three basic sequence types: lists, tuples, and range objects. Additional sequence types tailored for processing of 二进制数据 and 文本字符串 are described in dedicated sections.

    常见序列操作 ¶

    The operations in the following table are supported by most sequence types, both mutable and immutable. The collections.abc.Sequence ABC is provided to make it easier to correctly implement these operations on custom sequence types.

    This table lists the sequence operations sorted in ascending priority. In the table, s and t are sequences of the same type, n , i , j and k are integers and x is an arbitrary object that meets any type and value restrictions imposed by s .

    The in and not in operations have the same priorities as the comparison operations. The + (concatenation) and * (repetition) operations have the same priority as the corresponding numeric operations. [ 3 ]

    操作

    结果

    注意事项

    x in s

    True if an item of s 等于 x ，否则 False

    		(1)

    x not in s

    False if an item of s 等于 x ，否则 True

    		(1)

    s + t

    the concatenation of s and t

    		(6)(7)

    s * n or n * s

    equivalent to adding s to itself n times

    		(2)(7)

    s[i]

    i th item of s , origin 0

    		(3)

    s[i:j]

    slice of s from i to j

    		(3)(4)

    s[i:j:k]

    slice of s from i to j with step k

    		(3)(5)

    len(s)

    length of s

    min(s)

    smallest item of s

    max(s)

    largest item of s

    s.index(x[, i[, j]])

    index of the first occurrence of x in s (at or after index i and before index j )

    		(8)

    s.count(x)

    total number of occurrences of x in s

    Sequences of the same type also support comparisons. In particular, tuples and lists are compared lexicographically by comparing corresponding elements. This means that to compare equal, every element must compare equal and the two sequences must be of the same type and have the same length. (For full details see 比较 in the language reference.)

    Forward and reversed iterators over mutable sequences access values using an index. That index will continue to march forward (or backward) even if the underlying sequence is mutated. The iterator terminates only when an IndexError 或 StopIteration is encountered (or when the index drops below zero).

    注意事项：

    1. While the in and not in operations are used only for simple containment testing in the general case, some specialised sequences (such as str , bytes and bytearray ) also use them for subsequence testing: 

      >>> "gg" in "eggs"
True

    2. Values of n less than 0 are treated as 0 (which yields an empty sequence of the same type as s ). Note that items in the sequence s are not copied; they are referenced multiple times. This often haunts new Python programmers; consider: 

      >>> lists = [[]] * 3
>>> lists
[[], [], []]
>>> lists[0].append(3)
>>> lists
[[3], [3], [3]]

      What has happened is that [[]] is a one-element list containing an empty list, so all three elements of [[]] * 3 are references to this single empty list. Modifying any of the elements of lists modifies this single list. You can create a list of different lists this way: 

      >>> lists = [[] for i in range(3)]
>>> lists[0].append(3)
>>> lists[1].append(5)
>>> lists[2].append(7)
>>> lists
[[3], [5], [7]]

      Further explanation is available in the FAQ entry How do I create a multidimensional list? .

    3. 若 i or j is negative, the index is relative to the end of sequence s : len(s) + i or len(s) + j is substituted. But note that -0 仍然是 0 .

    4. The slice of s from i to j is defined as the sequence of items with index k 这样 i <= k < j 。若 i or j 大于 len(s) ，使用 len(s) 。若 i 被省略或 None ，使用 0 。若 j 被省略或 None ，使用 len(s) 。若 i >= j , the slice is empty.

    5. The slice of s from i to j with step k is defined as the sequence of items with index x = i + n*k 这样 0 <= n < (j-i)/k . In other words, the indices are i , i+k , i+2*k , i+3*k and so on, stopping when j is reached (but never including j ). When k is positive, i and j are reduced to len(s) if they are greater. When k 为负， i and j are reduced to len(s) - 1 if they are greater. If i or j are omitted or None , they become “end” values (which end depends on the sign of k ). Note, k cannot be zero. If k is None , it is treated like 1 .

    6. Concatenating immutable sequences always results in a new object. This means that building up a sequence by repeated concatenation will have a quadratic runtime cost in the total sequence length. To get a linear runtime cost, you must switch to one of the alternatives below:

      • if concatenating str objects, you can build a list and use str.join() at the end or else write to an io.StringIO instance and retrieve its value when complete

      • if concatenating bytes objects, you can similarly use bytes.join() or io.BytesIO , or you can do in-place concatenation with a bytearray 对象。 bytearray objects are mutable and have an efficient overallocation mechanism

      • if concatenating tuple objects, extend a list 代替

      • for other types, investigate the relevant class documentation

    7. Some sequence types (such as range ) only support item sequences that follow specific patterns, and hence don’t support sequence concatenation or repetition.

    8. index 引发 ValueError 当 x 找不到在 s . Not all implementations support passing the additional arguments i and j . These arguments allow efficient searching of subsections of the sequence. Passing the extra arguments is roughly equivalent to using s[i:j].index(x) , only without copying any data and with the returned index being relative to the start of the sequence rather than the start of the slice.

    不可变序列类型 ¶

    The only operation that immutable sequence types generally implement that is not also implemented by mutable sequence types is support for the hash() 内置。

    This support allows immutable sequences, such as tuple instances, to be used as dict keys and stored in set and frozenset 实例。

    Attempting to hash an immutable sequence that contains unhashable values will result in TypeError .

    可变序列类型 ¶

    The operations in the following table are defined on mutable sequence types. The collections.abc.MutableSequence ABC is provided to make it easier to correctly implement these operations on custom sequence types.

    In the table s is an instance of a mutable sequence type, t is any iterable object and x is an arbitrary object that meets any type and value restrictions imposed by s (例如， bytearray only accepts integers that meet the value restriction 0 <= x <= 255 ).

    操作

    结果

    注意事项

    s[i] = x

    item i of s 被替换通过 x

    s[i:j] = t

    slice of s from i to j is replaced by the contents of the iterable t

    del s[i:j]

    如同 s[i:j] = []

    s[i:j:k] = t

    the elements of s[i:j:k] are replaced by those of t

    		(1)

    del s[i:j:k]

    removes the elements of s[i:j:k] from the list

    s.append(x)

    追加 x 到序列末尾 (如同 s[len(s):len(s)] = [x] )

    s.clear()

    removes all items from s (same as del s[:] )

    		(5)

    s.copy()

    creates a shallow copy of s (same as s[:] )

    		(5)

    s.extend(t) or s += t

    extends s with the contents of t (for the most part the same as s[len(s):len(s)] = t )

    s *= n

    更新 s with its contents repeated n times

    		(6)

    s.insert(i, x)

    插入 x into s at the index given by i (same as s[i:i] = [x] )

    s.pop() or s.pop(i)

    retrieves the item at i and also removes it from s

    		(2)

    s.remove(x)

    remove the first item from s where s[i] 等于 x

    		(3)

    s.reverse()

    reverses the items of s in place

    		(4)

    注意事项：

    1. t 必须与要替换切片具有相同的长度。

    2. 可选自变量 i 默认为 -1 ，因此默认情况下，最后项会被移除并返回。

    3. remove() 引发 ValueError 当 x 找不到在 s .

    4. The reverse() method modifies the sequence in place for economy of space when reversing a large sequence. To remind users that it operates by side effect, it does not return the reversed sequence.

    5. clear() and copy() are included for consistency with the interfaces of mutable containers that don’t support slicing operations (such as dict and set ). copy() is not part of the collections.abc.MutableSequence ABC, but most concrete mutable sequence classes provide it.

      Added in version 3.3: clear() and copy() 方法。

    6. 值 n is an integer, or an object implementing __index__() . Zero and negative values of n clear the sequence. Items in the sequence are not copied; they are referenced multiple times, as explained for s * n under 常见序列操作 .

    列表 ¶

    列表是通常用于存储同构项 (其相似性的准确程度因应用程序不同而异) 的集合的可变序列。

    class list ( [ iterable ] ) ¶

    可以按几种方式构建列表：

    • 使用一对方括号表示空列表： []

    • 使用方括号，采用逗号分隔项： [a] , [a, b, c]

    • 使用列表推导： [x for x in iterable]

    • 使用类型构造函数： list() or list(iterable)

    The constructor builds a list whose items are the same and in the same order as iterable ’s items. iterable may be either a sequence, a container that supports iteration, or an iterator object. If iterable is already a list, a copy is made and returned, similar to iterable[:] 。例如， list('abc') 返回 ['a', 'b', 'c'] and list( (1, 2, 3) ) 返回 [1, 2, 3] . If no argument is given, the constructor creates a new empty list, [] .

    许多其它操作也产生列表，包括 sorted() 内置。

    列表实现了所有的 common and 可变 序列操作。列表还提供以下额外方法：

    sort ( * , key = None , reverse = False ) ¶

    此方法原位排序列表，仅使用 < 比较各项。不抑制异常 - 若任何比较操作失败，整个排序操作将失败 (和列表可能处于被部分修改的状态)。

    sort() 接受仅通过关键字传递的 2 自变量 ( 仅关键词自变量 ):

    key specifies a function of one argument that is used to extract a comparison key from each list element (for example, key=str.lower ). The key corresponding to each item in the list is calculated once and then used for the entire sorting process. The default value of None means that list items are sorted directly without calculating a separate key value.

    The functools.cmp_to_key() utility is available to convert a 2.x style cmp 函数到 key 函数。

    reverse 是布尔值。若设为 True ，则对列表元素排序，就好像反转每一比较。

    This method modifies the sequence in place for economy of space when sorting a large sequence. To remind users that it operates by side effect, it does not return the sorted sequence (use sorted() to explicitly request a new sorted list instance).

    The sort() method is guaranteed to be stable. A sort is stable if it guarantees not to change the relative order of elements that compare equal — this is helpful for sorting in multiple passes (for example, sort by department, then by salary grade).

    对于排序范例和简短排序教程，见 Sorting Techniques .

    CPython 实现细节： While a list is being sorted, the effect of attempting to mutate, or even inspect, the list is undefined. The C implementation of Python makes the list appear empty for the duration, and raises ValueError if it can detect that the list has been mutated during a sort.

    元组 ¶

    Tuples are immutable sequences, typically used to store collections of heterogeneous data (such as the 2-tuples produced by the enumerate() built-in). Tuples are also used for cases where an immutable sequence of homogeneous data is needed (such as allowing storage in a set or dict 实例)。

    class tuple ( [ iterable ] ) ¶

    可以按多种方式构建元组：

    • Using a pair of parentheses to denote the empty tuple: ()

    • Using a trailing comma for a singleton tuple: a, or (a,)

    • 采用逗号分隔项： a, b, c or (a, b, c)

    • 使用 tuple() 内置： tuple() or tuple(iterable)

    The constructor builds a tuple whose items are the same and in the same order as iterable ’s items. iterable may be either a sequence, a container that supports iteration, or an iterator object. If iterable is already a tuple, it is returned unchanged. For example, tuple('abc') 返回 ('a', 'b', 'c') and tuple( [1, 2, 3] ) 返回 (1, 2, 3) . If no argument is given, the constructor creates a new empty tuple, () .

    Note that it is actually the comma which makes a tuple, not the parentheses. The parentheses are optional, except in the empty tuple case, or when they are needed to avoid syntactic ambiguity. For example, f(a, b, c) is a function call with three arguments, while f((a, b, c)) is a function call with a 3-tuple as the sole argument.

    元组实现了所有的 common 序列操作。

    For heterogeneous collections of data where access by name is clearer than access by index, collections.namedtuple() may be a more appropriate choice than a simple tuple object.

    范围 ¶

    The range type represents an immutable sequence of numbers and is commonly used for looping a specific number of times in for 循环。

    class range ( stop ) ¶
    class range ( start , stop [ , step ] )

    The arguments to the range constructor must be integers (either built-in int or any object that implements the __index__() special method). If the step argument is omitted, it defaults to 1 。若 start argument is omitted, it defaults to 0 。若 step 为 0， ValueError 被引发。

    对于正值 step , the contents of a range r are determined by the formula r[i] = start + step*i where i >= 0 and r[i] < stop .

    对于负值 step , the contents of the range are still determined by the formula r[i] = start + step*i , but the constraints are i >= 0 and r[i] > stop .

    A range object will be empty if r[0] does not meet the value constraint. Ranges do support negative indices, but these are interpreted as indexing from the end of the sequence determined by the positive indices.

    range 包含的绝对值 > sys.maxsize 准许，但某些特征 (譬如 len() ) 可能引发 OverflowError .

    范围范例： 

    >>> list(range(10))
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> list(range(1, 11))
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
>>> list(range(0, 30, 5))
[0, 5, 10, 15, 20, 25]
>>> list(range(0, 10, 3))
[0, 3, 6, 9]
>>> list(range(0, -10, -1))
[0, -1, -2, -3, -4, -5, -6, -7, -8, -9]
>>> list(range(0))
[]
>>> list(range(1, 0))
[]

    range 实现了所有的 common sequence operations except concatenation and repetition (due to the fact that range objects can only represent sequences that follow a strict pattern and repetition and concatenation will usually violate that pattern).

    start ¶

    值对于 start 参数 (或 0 若参数未供给)

    stop ¶

    值对于 stop 参数

    step ¶

    值对于 step 参数 (或 1 若参数未供给)

    The advantage of the range type over a regular list or tuple is that a range object will always take the same (small) amount of memory, no matter the size of the range it represents (as it only stores the start , stop and step values, calculating individual items and subranges as needed).

    Range objects implement the collections.abc.Sequence ABC, and provide features such as containment tests, element index lookup, slicing and support for negative indices (see 序列类型 — 列表、元组、范围 ): 

    >>> r = range(0, 20, 2)
>>> r
range(0, 20, 2)
>>> 11 in r
False
>>> 10 in r
True
>>> r.index(10)
5
>>> r[5]
10
>>> r[:5]
range(0, 10, 2)
>>> r[-1]
18

    Testing range objects for equality with == and != compares them as sequences. That is, two range objects are considered equal if they represent the same sequence of values. (Note that two range objects that compare equal might have different start , stop and step attributes, for example range(0) == range(2, 1, 3) or range(0, 3, 2) == range(0, 4, 2) )。

    3.2 版改变： Implement the Sequence ABC. Support slicing and negative indices. Test int objects for membership in constant time instead of iterating through all items.

    3.3 版改变： Define ‘==’ and ‘!=’ to compare range objects based on the sequence of values they define (instead of comparing based on object identity).

    添加 start , stop and step 属性。

    另请参阅

    • The linspace recipe shows how to implement a lazy version of range suitable for floating point applications.

    文本序列类型 — str ¶

    Python 正文数据的处理是采用 str 对象，或 strings 。字符串是不可变 sequences 的 Unicode 代码点。字符串文字以多种方式编写：

    • 单引号： 'allows embedded "double" quotes'

    • 双引号： "allows embedded 'single' quotes"

    • 三引号： '''Three single quotes''' , """Three double quotes"""

    3 引号字符串可以跨多行 - 所有关联空白都将包括在字符串文字中。

    属于单个表达式且它们之间只有空白的字符串文字，将被隐式转换成单字符串文字。也就是说, ("spam " "eggs") == "spam eggs" .

    见 字符串和 bytes 文字 for more about the various forms of string literal, including supported escape sequences ，和 r (“raw”) prefix that disables most escape sequence processing.

    也可以从其它对象创建字符串，使用 str 构造函数。

    由于不存在单独 "字符" 类型，索引字符串会产生 1 长字符串。也就是说，对于非空字符串 s , s[0] == s[0:1] .

    也不存在可变字符串类型，但 str.join() or io.StringIO 可以用于从多个片段，高效构造字符串。

    3.3 版改变： For backwards compatibility with the Python 2 series, the u prefix is once again permitted on string literals. It has no effect on the meaning of string literals and cannot be combined with the r 前缀。

    class str ( object = '' ) ¶
    class str ( object = b'' , encoding = 'utf-8' , errors = 'strict' )

    返回 string 版本的 object 。若 object 不提供，返回空字符串。否则，行为在 str() 从属是否 encoding or errors 有给定，如下所示。

    若 encoding nor errors 有给定， str(object) 返回 type(object).__str__(object) ，这是非正式或很好可打印字符串表示的 object 。对于字符串对象，这是字符串自身。若 object 没有 __str__() 方法，那么 str() 回退以返回 repr(object) .

    若至少某一 encoding or errors 有给定， object 应该为 像字节对象 (如 bytes or bytearray )。在此情况下，若 object 是 bytes (或 bytearray ) 对象，那么 str(bytes, encoding, errors) 相当于 bytes.decode(encoding, errors) 。否则，获取缓冲对象的底层字节对象，先于调用 bytes.decode() 。见 二进制序列类型 — 字节、字节数组、内存视图 and 缓冲协议 了解缓冲对象有关信息。

    传递 bytes 对象到 str() 不带 encoding or errors 自变量属于返回非正式字符串表示的第一种情况 (另请参阅 -b 命令行选项到 Python)。例如： 

    >>> str(b'Zoot!')
"b'Zoot!'"

    对于更多信息有关 str 类及其方法，见 文本序列类型 — str 和 字符串方法 下文章节。要输出格式化字符串，见 f-strings and 格式字符串语法 章节。此外，见 文本处理服务 章节。

    字符串方法 ¶

    字符串实现了所有的 common 序列操作，及额外方法的描述见下文。

    Strings also support two styles of string formatting, one providing a large degree of flexibility and customization (see str.format() , 格式字符串语法 and 自定义字符串格式化 ) and the other based on C printf style formatting that handles a narrower range of types and is slightly harder to use correctly, but is often faster for the cases it can handle ( printf 样式字符串格式化 ).

    The 文本处理服务 section of the standard library covers a number of other modules that provide various text related utilities (including regular expression support in the re 模块)。

    str. capitalize ( ) ¶

    返回第一个字符大写和其余小写的字符串副本。

    3.8 版改变： 第一个字符现在放入标题大小写，而不是大写。这意味着像连字符将只大写第一个字母，而不是完整字符。

    str. casefold ( ) ¶

    返回字符串的大小写折叠副本。大小写折叠字符串可以用于无大小写匹配。

    Casefolding is similar to lowercasing but more aggressive because it is intended to remove all case distinctions in a string. For example, the German lowercase letter 'ß' 相当于 "ss" . Since it is already lowercase, lower() would do nothing to 'ß' ; casefold() converts it to "ss" .

    The casefolding algorithm is described in section 3.13 ‘Default Case Folding’ of the Unicode Standard .

    Added in version 3.3.

    str. center ( width [ , fillchar ] ) ¶

    返回居中字符串按长度 width 。铺垫的履行是使用指定 fillchar (默认为 ASCII 空格)。返回原始字符串若 width <= len(s) .

    str. count ( sub [ , start [ , end ] ] ) ¶

    返回非重叠出现次数对于子字符串 sub 在范围 [ start , end ]。可选自变量 start and end 按切片表示法解释。

    若 sub is empty, returns the number of empty strings between characters which is the length of the string plus one.

    str. encode ( encoding = 'utf-8' , errors = 'strict' ) ¶

    Return the string encoded to bytes .

    encoding 默认为 'utf-8' ；见 标准编码 了解可能值。

    errors controls how encoding errors are handled. If 'strict' (默认)， UnicodeError exception is raised. Other possible values are 'ignore' , 'replace' , 'xmlcharrefreplace' , 'backslashreplace' 及任何其它名称注册凭借 codecs.register_error() 。见 错误处理程序 了解细节。

    For performance reasons, the value of errors is not checked for validity unless an encoding error actually occurs, Python 开发模式 is enabled or a 调试构建 被使用。

    3.1 版改变： 添加支持关键词自变量。

    3.9 版改变： 值对于 errors argument is now checked in Python 开发模式 和在 调试模式 .

    str. endswith ( suffix [ , start [ , end ] ] ) ¶

    返回 True 若字符串结束采用指定 suffix ，否则返回 False . suffix can also be a tuple of suffixes to look for. With optional start , test beginning at that position. With optional end , stop comparing at that position.

    str. expandtabs ( tabsize = 8 ) ¶

    返回以一个或多个空格替换所有 Tab 的字符串副本，从属当前列和给定的 Tab (制表符) 大小。制表符位置出现每 tabsize characters (default is 8, giving tab positions at columns 0, 8, 16 and so on). To expand the string, the current column is set to zero and the string is examined character by character. If the character is a tab ( \t ), one or more space characters are inserted in the result until the current column is equal to the next tab position. (The tab character itself is not copied.) If the character is a newline ( \n ) 或返回 ( \r ), it is copied and the current column is reset to zero. Any other character is copied unchanged and the current column is incremented by one regardless of how the character is represented when printed. 

    >>> '01\t012\t0123\t01234'.expandtabs()
'01      012     0123    01234'
>>> '01\t012\t0123\t01234'.expandtabs(4)
'01  012 0123    01234'
    str. find ( sub [ , start [ , end ] ] ) ¶

    返回在字符串中的最低索引，其中子字符串 sub 被找到在切片 s[start:end] 。可选自变量 start and end 按切片表示法解释。返回 -1 if sub 找不到。

    注意

    The find() 方法才应被使用，若需要知道位置为 sub 。要校验若 sub 是子字符串或不是，使用 in 运算符： 

    >>> 'Py' in 'Python'
True
    str. format ( * args , ** kwargs ) ¶

    Perform a string formatting operation. The string on which this method is called can contain literal text or replacement fields delimited by braces {} . Each replacement field contains either the numeric index of a positional argument, or the name of a keyword argument. Returns a copy of the string where each replacement field is replaced with the string value of the corresponding argument. 

    >>> "The sum of 1 + 2 is {0}".format(1+2)
'The sum of 1 + 2 is 3'

    见 格式字符串语法 for a description of the various formatting options that can be specified in format strings.

    注意

    当格式化数字 ( int , float , complex , decimal.Decimal 及子类) 采用 n 类型 (范例： '{:n}'.format(1234) )，函数临时设置 LC_CTYPE 区域设置到 LC_NUMERIC 区域设置以解码 decimal_point and thousands_sep fields of localeconv() if they are non-ASCII or longer than 1 byte, and the LC_NUMERIC locale is different than the LC_CTYPE locale. This temporary change affects other threads.

    3.7 版改变： 当格式化数字采用 n 类型，函数设置临时 LC_CTYPE 区域设置到 LC_NUMERIC 区域设置在某些情况下。

    str. format_map ( 映射 ) ¶

    类似于 str.format(**mapping) ，除了 mapping 的直接使用而不是拷贝到 dict 。这很有用，例如若 mapping 是 dict 子类： 

    >>> class Default(dict):
...     def __missing__(self, key):
...         return key
...
>>> '{name} was born in {country}'.format_map(Default(name='Guido'))
'Guido was born in country'

    Added in version 3.2.

    str. index ( sub [ , start [ , end ] ] ) ¶

    像 find() ，但会引发 ValueError 当找不到子字符串时。

    str. isalnum ( ) ¶

    返回 True 若字符串中的所有字符都是字母数字且至少有 1 个字符， False 否则。字符 c 是字母数字若下列之一返回 True : c.isalpha() , c.isdecimal() , c.isdigit() ，或 c.isnumeric() .

    str. isalpha ( ) ¶

    返回 True 若字符串中的所有字符都是字母，且至少有 1 字符， False otherwise. Alphabetic characters are those characters defined in the Unicode character database as “Letter”, i.e., those with general category property being one of “Lm”, “Lt”, “Lu”, “Ll”, or “Lo”. Note that this is different from the Alphabetic property defined in the section 4.10 ‘Letters, Alphabetic, and Ideographic’ of the Unicode Standard .

    str. isascii ( ) ¶

    返回 True 若字符串为空或字符串中的所有字符都是 ASCII， False 否则。ASCII 字符的代码点在 U+0000-U+007F 范围内。

    Added in version 3.7.

    str. isdecimal ( ) ¶

    返回 True if all characters in the string are decimal characters and there is at least one character, False otherwise. Decimal characters are those that can be used to form numbers in base 10, e.g. U+0660, ARABIC-INDIC DIGIT ZERO. Formally a decimal character is a character in the Unicode General Category “Nd”.

    str. isdigit ( ) ¶

    返回 True 若字符串中的所有字符都是数字且至少有一个字符， False otherwise. Digits include decimal characters and digits that need special handling, such as the compatibility superscript digits. This covers digits which cannot be used to form numbers in base 10, like the Kharosthi numbers. Formally, a digit is a character that has the property value Numeric_Type=Digit or Numeric_Type=Decimal.

    str. isidentifier ( ) ¶

    返回 True 若字符串是根据语言定义的有效标识符，章节 标识符和关键词 .

    keyword.iskeyword() can be used to test whether string s 是预留标识符，譬如 def and class .

    范例： 

    >>> from keyword import iskeyword
>>> 'hello'.isidentifier(), iskeyword('hello')
(True, False)
>>> 'def'.isidentifier(), iskeyword('def')
(True, True)
    str. islower ( ) ¶

    返回 True 若所有大小写字符 [ 4 ] in the string are lowercase and there is at least one cased character, False 否则。

    str. isnumeric ( ) ¶

    返回 True if all characters in the string are numeric characters, and there is at least one character, False otherwise. Numeric characters include digit characters, and all characters that have the Unicode numeric value property, e.g. U+2155, VULGAR FRACTION ONE FIFTH. Formally, numeric characters are those with the property value Numeric_Type=Digit, Numeric_Type=Decimal or Numeric_Type=Numeric.

    str. isprintable ( ) ¶

    返回 True if all characters in the string are printable or the string is empty, False otherwise. Nonprintable characters are those characters defined in the Unicode character database as “Other” or “Separator”, excepting the ASCII space (0x20) which is considered printable. (Note that printable characters in this context are those which should not be escaped when repr() is invoked on a string. It has no bearing on the handling of strings written to sys.stdout or sys.stderr )。

    str. isspace ( ) ¶

    返回 True if there are only whitespace characters in the string and there is at least one character, False 否则。

    A character is whitespace if in the Unicode character database (see unicodedata ), either its general category is Zs (“Separator, space”), or its bidirectional class is one of WS , B ，或 S .

    str. istitle ( ) ¶

    返回 True if the string is a titlecased string and there is at least one character, for example uppercase characters may only follow uncased characters and lowercase characters only cased ones. Return False 否则。

    str. isupper ( ) ¶

    返回 True 若所有大小写字符 [ 4 ] in the string are uppercase and there is at least one cased character, False 否则。 

    >>> 'BANANA'.isupper()
True
>>> 'banana'.isupper()
False
>>> 'baNana'.isupper()
False
>>> ' '.isupper()
False
    str. join ( iterable ) ¶

    Return a string which is the concatenation of the strings in iterable 。 TypeError will be raised if there are any non-string values in iterable ，包括 bytes objects. The separator between elements is the string providing this method.

    str. ljust ( width [ , fillchar ] ) ¶

    返回字符串的左对齐字符串按长度 width 。铺垫的履行是使用指定 fillchar (默认为 ASCII 空格)。返回原始字符串若 width <= len(s) .

    str. lower ( ) ¶

    返回的字符串副本具有所有大小写字符 [ 4 ] 被转换成小写。

    The lowercasing algorithm used is described in section 3.13 ‘Default Case Folding’ of the Unicode Standard .

    str. lstrip ( [ chars ] ) ¶

    返回移除前导字符的字符串拷贝。 chars 自变量是指定要移除字符集的字符串。若省略或 None ， chars 自变量默认为移除空白。 chars 自变量不是前缀；在一定程度上，会剥离其值的所有组合： 

    >>> '   spacious   '.lstrip()
'spacious   '
>>> 'www.example.com'.lstrip('cmowz.')
'example.com'

    见 str.removeprefix() for a method that will remove a single prefix string rather than all of a set of characters. For example: 

    >>> 'Arthur: three!'.lstrip('Arthur: ')
'ee!'
>>> 'Arthur: three!'.removeprefix('Arthur: ')
'three!'
    static str. maketrans ( x [ , y [ , z ] ] ) ¶

    此静态方法返回的翻译表可用于 str.translate() .

    If there is only one argument, it must be a dictionary mapping Unicode ordinals (integers) or characters (strings of length 1) to Unicode ordinals, strings (of arbitrary lengths) or None . Character keys will then be converted to ordinals.

    If there are two arguments, they must be strings of equal length, and in the resulting dictionary, each character in x will be mapped to the character at the same position in y. If there is a third argument, it must be a string, whose characters will be mapped to None in the result.

    str. partition ( sep ) ¶

    Split the string at the first occurrence of sep , and return a 3-tuple containing the part before the separator, the separator itself, and the part after the separator. If the separator is not found, return a 3-tuple containing the string itself, followed by two empty strings.

    str. removeprefix ( prefix , / ) ¶

    若字符串开始采用 prefix 字符串，返回 string[len(prefix):] 。否则，返回原始字符串的副本： 

    >>> 'TestHook'.removeprefix('Test')
'Hook'
>>> 'BaseTestCase'.removeprefix('Test')
'BaseTestCase'

    Added in version 3.9.

    str. removesuffix ( suffix , / ) ¶

    若字符串结束采用 suffix 字符串和 suffix 不为空，返回 string[:-len(suffix)] 。否则，返回原始字符串的副本： 

    >>> 'MiscTests'.removesuffix('Tests')
'Misc'
>>> 'TmpDirMixin'.removesuffix('Tests')
'TmpDirMixin'

    Added in version 3.9.

    str. replace ( old , new [ , count ] ) ¶

    返回字符串副本具有所有出现的子字符串 old 被替换通过 new 。若可选自变量 count 有给定，仅前 count 出现被替换。

    str. rfind ( sub [ , start [ , end ] ] ) ¶

    返回字符串中的最高索引，若子字符串 sub 被发现，这种 sub 包含在 s[start:end] 。可选自变量 start and end 按切片表示法解释。返回 -1 当故障时。

    str. rindex ( sub [ , start [ , end ] ] ) ¶

    像 rfind() 但引发 ValueError 当子字符串 sub 找不到。

    str. rjust ( width [ , fillchar ] ) ¶

    返回字符串的右对齐字符串按长度 width 。铺垫的履行是使用指定 fillchar (默认为 ASCII 空格)。返回原始字符串若 width <= len(s) .

    str. rpartition ( sep ) ¶

    Split the string at the last occurrence of sep , and return a 3-tuple containing the part before the separator, the separator itself, and the part after the separator. If the separator is not found, return a 3-tuple containing two empty strings, followed by the string itself.

    str. rsplit ( sep = None , maxsplit = -1 ) ¶

    返回字符串中单词的列表，使用 sep 作为定界符字符串。若 maxsplit is given, at most maxsplit splits are done, the rightmost ones. If sep 未指定或 None , any whitespace string is a separator. Except for splitting from the right, rsplit() behaves like split() which is described in detail below.

    str. rstrip ( [ chars ] ) ¶

    返回移除结尾字符的字符串拷贝。 chars 自变量是指定要移除字符集的字符串。若省略或 None ， chars 自变量默认为移除空白。 chars 自变量不是后缀；在一定程度上，会剥离其值的所有组合： 

    >>> '   spacious   '.rstrip()
'   spacious'
>>> 'mississippi'.rstrip('ipz')
'mississ'

    见 str.removesuffix() for a method that will remove a single suffix string rather than all of a set of characters. For example: 

    >>> 'Monty Python'.rstrip(' Python')
'M'
>>> 'Monty Python'.removesuffix(' Python')
'Monty'
    str. split ( sep = None , maxsplit = -1 ) ¶

    返回字符串中单词的列表，使用 sep 作为定界符字符串。若 maxsplit is given, at most maxsplit splits are done (thus, the list will have at most maxsplit+1 elements). If maxsplit 未指定或 -1 , then there is no limit on the number of splits (all possible splits are made).

    若 sep is given, consecutive delimiters are not grouped together and are deemed to delimit empty strings (for example, '1,,2'.split(',') 返回 ['1', '', '2'] )。 sep argument may consist of multiple characters (for example, '1<>2<>3'.split('<>') 返回 ['1', '2', '3'] ). Splitting an empty string with a specified separator returns [''] .

    例如： 

    >>> '1,2,3'.split(',')
['1', '2', '3']
>>> '1,2,3'.split(',', maxsplit=1)
['1', '2,3']
>>> '1,2,,3,'.split(',')
['1', '2', '', '3', '']

    若 sep 未指定或是 None , a different splitting algorithm is applied: runs of consecutive whitespace are regarded as a single separator, and the result will contain no empty strings at the start or end if the string has leading or trailing whitespace. Consequently, splitting an empty string or a string consisting of just whitespace with a None separator returns [] .

    例如： 

    >>> '1 2 3'.split()
['1', '2', '3']
>>> '1 2 3'.split(maxsplit=1)
['1', '2 3']
>>> '   1   2   3   '.split()
['1', '2', '3']
    str. splitlines ( keepends = False ) ¶

    Return a list of the lines in the string, breaking at line boundaries. Line breaks are not included in the resulting list unless keepends is given and true.

    This method splits on the following line boundaries. In particular, the boundaries are a superset of 通用换行符 .

    表示

    描述

    \n

    		换行

    \r

    		CR (回车)

    \r\n

    		Carriage Return + Line Feed

    \v or \x0b

    		Line Tabulation

    \f or \x0c

    		换页

    \x1c

    		文件分隔符

    \x1d

    		组分隔符

    \x1e

    		记录分隔符

    \x85

    		Next Line (C1 Control Code)

    \u2028

    		行分隔符

    \u2029

    		段落分隔符

    3.2 版改变： \v and \f 被添加到行边界列表。

    例如： 

    >>> 'ab c\n\nde fg\rkl\r\n'.splitlines()
['ab c', '', 'de fg', 'kl']
>>> 'ab c\n\nde fg\rkl\r\n'.splitlines(keepends=True)
['ab c\n', '\n', 'de fg\r', 'kl\r\n']

    不像 split() when a delimiter string sep is given, this method returns an empty list for the empty string, and a terminal line break does not result in an extra line: 

    >>> "".splitlines()
[]
>>> "One line\n".splitlines()
['One line']

    为比较， split('\n') gives: 

    >>> ''.split('\n')
['']
>>> 'Two lines\n'.split('\n')
['Two lines', '']
    str. startswith ( prefix [ , start [ , end ] ] ) ¶

    返回 True 若字符串开始采用 prefix ，否则返回 False . prefix can also be a tuple of prefixes to look for. With optional start , test string beginning at that position. With optional end , stop comparing string at that position.

    str. strip ( [ chars ] ) ¶

    Return a copy of the string with the leading and trailing characters removed. The chars 自变量是指定要移除字符集的字符串。若省略或 None ， chars 自变量默认为移除空白。 chars 自变量不是前缀 (或后缀)；在一定程度上，会剥离其值的所有组合： 

    >>> '   spacious   '.strip()
'spacious'
>>> 'www.example.com'.strip('cmowz.')
'example'

    最外侧的前导和结尾 chars argument values are stripped from the string. Characters are removed from the leading end until reaching a string character that is not contained in the set of characters in chars . A similar action takes place on the trailing end. For example: 

    >>> comment_string = '#....... Section 3.2.1 Issue #32 .......'
>>> comment_string.strip('.#! ')
'Section 3.2.1 Issue #32'
    str. swapcase ( ) ¶

    Return a copy of the string with uppercase characters converted to lowercase and vice versa. Note that it is not necessarily true that s.swapcase().swapcase() == s .

    str. title ( ) ¶

    返回字符串的首字母大写版本，单词以大写字符开头，其余字符为小写。

    例如： 

    >>> 'Hello world'.title()
'Hello World'

    The algorithm uses a simple language-independent definition of a word as groups of consecutive letters. The definition works in many contexts but it means that apostrophes in contractions and possessives form word boundaries, which may not be the desired result: 

    >>> "they're bill's friends from the UK".title()
"They'Re Bill'S Friends From The Uk"

    The string.capwords() function does not have this problem, as it splits words on spaces only.

    Alternatively, a workaround for apostrophes can be constructed using regular expressions: 

    >>> import re
>>> def titlecase(s):
...     return re.sub(r"[A-Za-z]+('[A-Za-z]+)?",
...                   lambda mo: mo.group(0).capitalize(),
...                   s)
...
>>> titlecase("they're bill's friends.")
"They're Bill's Friends."
    str. translate ( table ) ¶

    Return a copy of the string in which each character has been mapped through the given translation table. The table must be an object that implements indexing via __getitem__() , typically a 映射 or sequence . When indexed by a Unicode ordinal (an integer), the table object can do any of the following: return a Unicode ordinal or a string, to map the character to one or more other characters; return None , to delete the character from the return string; or raise a LookupError exception, to map the character to itself.

    可以使用 str.maketrans() to create a translation map from character-to-character mappings in different formats.

    另请参阅 codecs module for a more flexible approach to custom character mappings.

    str. upper ( ) ¶

    返回的字符串副本具有所有大小写字符 [ 4 ] 被转换成大写。注意， s.upper().isupper() 可以是 False if s contains uncased characters or if the Unicode category of the resulting character(s) is not “Lu” (Letter, uppercase), but e.g. “Lt” (Letter, titlecase).

    The uppercasing algorithm used is described in section 3.13 ‘Default Case Folding’ of the Unicode Standard .

    str. zfill ( width ) ¶

    返回字符串的副本左侧填充采用 ASCII '0' digits to make a string of length width . A leading sign prefix ( '+' / '-' ) is handled by inserting the padding after the sign character rather than before. The original string is returned if width <= len(s) .

    例如： 

    >>> "42".zfill(5)
'00042'
>>> "-42".zfill(5)
'-0042'

    printf 样式字符串格式化 ¶

    注意

    The formatting operations described here exhibit a variety of quirks that lead to a number of common errors (such as failing to display tuples and dictionaries correctly). Using the newer 格式化字符串文字 ， str.format() 接口，或 模板字符串 may help avoid these errors. Each of these alternatives provides their own trade-offs and benefits of simplicity, flexibility, and/or extensibility.

    String objects have one unique built-in operation: the % operator (modulo). This is also known as the string formatting or interpolation operator. Given format % values (在哪里 format 是字符串)， % conversion specifications in format are replaced with zero or more elements of 值 . The effect is similar to using the sprintf() 在 C 语言中。

    若 format requires a single argument, 值 may be a single non-tuple object. [ 5 ] 否则， 值 must be a tuple with exactly the number of items specified by the format string, or a single mapping object (for example, a dictionary).

    A conversion specifier contains two or more characters and has the following components, which must occur in this order:

    1. The '%' character, which marks the start of the specifier.

    2. Mapping key (optional), consisting of a parenthesised sequence of characters (for example, (somename) ).

    3. Conversion flags (optional), which affect the result of some conversion types.

    4. Minimum field width (optional). If specified as an '*' (asterisk), the actual width is read from the next element of the tuple in 值 , and the object to convert comes after the minimum field width and optional precision.

    5. Precision (optional), given as a '.' (dot) followed by the precision. If specified as '*' (an asterisk), the actual precision is read from the next element of the tuple in 值 , and the value to convert comes after the precision.

    6. Length modifier (optional).

    7. 转换类型。

    When the right argument is a dictionary (or other mapping type), then the formats in the string must include a parenthesised mapping key into that dictionary inserted immediately after the '%' character. The mapping key selects the value to be formatted from the mapping. For example: 

    >>> print('%(language)s has %(number)03d quote types.' %
...       {'language': "Python", "number": 2})
Python has 002 quote types.

    In this case no * specifiers may occur in a format (since they require a sequential parameter list).

    转换标志字符：

    标志

    含义

    '#'

    The value conversion will use the “alternate form” (where defined below).

    '0'

    		The conversion will be zero padded for numeric values.

    '-'

    The converted value is left adjusted (overrides the '0' conversion if both are given).

    ' '

    (a space) A blank should be left before a positive number (or empty string) produced by a signed conversion.

    '+'

    A sign character ( '+' or '-' ) will precede the conversion (overrides a “space” flag).

    A length modifier ( h , l ，或 L ) may be present, but is ignored as it is not necessary for Python – so e.g. %ld is identical to %d .

    转换类型：

    转换

    含义

    注意事项

    'd'

    		有符号整数十进制。

    'i'

    		有符号整数十进制。

    'o'

    		有符号八进制值。 (1)

    'u'

    过时 type – 它等同于 'd' .

    		(6)

    'x'

    		有符号十六进制 (小写)。 (2)

    'X'

    		有符号十六进制 (大写)。 (2)

    'e'

    		浮点指数格式 (小写)。 (3)

    'E'

    		浮点指数格式 (大写)。 (3)

    'f'

    		浮点十进制格式。 (3)

    'F'

    		浮点十进制格式。 (3)

    'g'

    Floating point format. Uses lowercase exponential format if exponent is less than -4 or not less than precision, decimal format otherwise.

    		(4)

    'G'

    Floating point format. Uses uppercase exponential format if exponent is less than -4 or not less than precision, decimal format otherwise.

    		(4)

    'c'

    Single character (accepts integer or single character string).

    'r'

    字符串 (转换任何 Python 对象使用 repr() ).

    		(5)

    's'

    字符串 (转换任何 Python 对象使用 str() ).

    		(5)

    'a'

    字符串 (转换任何 Python 对象使用 ascii() ).

    		(5)

    '%'

    No argument is converted, results in a '%' character in the result.

    注意事项：

    1. The alternate form causes a leading octal specifier ( '0o' ) to be inserted before the first digit.

    2. The alternate form causes a leading '0x' or '0X' (depending on whether the 'x' or 'X' format was used) to be inserted before the first digit.

    3. The alternate form causes the result to always contain a decimal point, even if no digits follow it.

      The precision determines the number of digits after the decimal point and defaults to 6.

    4. The alternate form causes the result to always contain a decimal point, and trailing zeroes are not removed as they would otherwise be.

      The precision determines the number of significant digits before and after the decimal point and defaults to 6.

    5. 若精度为 N ，会截取输出成 N 字符。

    6. 见 PEP 237 .

    由于 Python 字符串有明确长度， %s 转换未假定 '\0' 是字符串末尾。

    3.1 版改变： %f 转换对于绝对值大于 1e50 的数字不再替换通过 %g 转换。

    二进制序列类型 — bytes , bytearray , memoryview ¶

    操纵二进制数据的核心内置类型是 bytes and bytearray 。它们的支持是通过 memoryview 使用 缓冲协议 访问其它二进制对象的内存 (无需制作拷贝)。

    The array 模块支持基本数据类型的高效存储，像 32 位整数和 IEEE754 双精度浮点值。

    bytes 对象 ¶

    bytes 对象是单字节的不可变序列。由于很多主要二进制协议均基于 ASCII 文本编码，因此 bytes 对象提供的几个方法才有效，当操控 ASCII 兼容数据并以各种其它方式密切相关字符串对象时。

    class bytes ( [ source [ , encoding [ , errors ] ] ] ) ¶

    首先，用于字节文字的句法很大程度上与用于字符串文字的一样，除了 b 前缀的添加：

    • 单引号： b'still allows embedded "double" quotes'

    • 双引号： b"still allows embedded 'single' quotes"

    • 三引号： b'''3 single quotes''' , b"""3 double quotes"""

    仅 ASCII 字符准许在 bytes 文字中 (不管声明源代码的编码)。大于 127 的任何二进制值，必须使用适当转义序列将其录入成 bytes 文字。

    如采用字符串文字，bytes 文字还可以使用 r 前缀以禁用转义序列的处理。见 字符串和 bytes 文字 了解各种形式字节文字的有关更多信息，包括支持的转义序列。

    bytes 文字及其表示虽然基于 ASCII 文本，但 bytes 对象的实际行为却像不可变整数序列，序列中的每个值均有限定，譬如 0 <= x < 256 (试图违反此限定将触发 ValueError )。这样做是故意强调虽然很多二进制格式包括基于 ASCII 的元素，且采用一些面向文本的操纵算法可能很有用，但对于任意二进制数据，一般来说却并非如此 (盲目将文本处理算法应用于不兼容 ASCII 的二进制数据格式，通常会导致数据破坏)。

    除文字形式外，还可以按很多其它方式创建 bytes 对象：

    • 指定长度的 0 填充 bytes 对象： bytes(10)

    • 来自整数迭代： bytes(range(20))

    • 凭借缓冲协议拷贝现有二进制数据： bytes(obj)

    另请参阅 bytes 内置。

    由于 2 个十六进制数字准确对应 1 个字节，因此，十六进制数字是用于描述二进制数据的常用格式。故此，bytes 类型有读取此种格式数据的额外类方法：

    classmethod fromhex ( string ) ¶

    This bytes 类方法解码给定字符串对象, 返回 bytes 对象。字符串每字节必须包含 2 十六进制数字，忽略 ASCII 空格。 

    >>> bytes.fromhex('2Ef0 F1f2  ')
b'.\xf0\xf1\xf2'

    3.7 版改变： bytes.fromhex() 现在跳过字符串中的所有 ASCII 空白，不仅仅空格。

    存在反向转换函数，能把 bytes 对象转换成其十六进制表示。

    hex ( [ sep [ , bytes_per_sep ] ] ) ¶

    返回字符串对象，实例包含每字节 2 十六进制数字。 

    >>> b'\xf0\xf1\xf2'.hex()
'f0f1f2'

    若想要使十六进制字符串更容易阅读，可以指定单个字符分隔符 sep parameter to include in the output. By default, this separator will be included between each byte. A second optional bytes_per_sep 参数控制间距。正值从右侧起计算分隔符位置，负值从左侧起计算分隔符位置。 

    >>> value = b'\xf0\xf1\xf2'
>>> value.hex('-')
'f0-f1-f2'
>>> value.hex('_', 2)
'f0_f1f2'
>>> b'UUDDLRLRAB'.hex(' ', -4)
'55554444 4c524c52 4142'

    Added in version 3.5.

    3.8 版改变： bytes.hex() 现在支持可选 sep and bytes_per_sep 参数以在十六进制输出的字节之间插入分隔符。

    由于 bytes 对象是整数序列 (类似于 tuple)，对于 bytes 对象 b , b[0] 将是整数，而 b[0:1] 将是长度为 1 的 bytes 对象 (相比之下，文本字符串的索引和切片两者均会产生长度为 1 的字符串)。

    bytes 对象的表示是使用文字格式 ( b'...' ) 因为它通常更有用，比如 bytes([46, 46, 46]) 。可以始终转换 bytes 对象成整数列表使用 list(b) .

    bytearray 对象 ¶

    bytearray 对象是可变搭档对于 bytes 对象。

    class bytearray ( [ source [ , encoding [ , errors ] ] ] ) ¶

    字节数组对象没有专用文字句法，相反，始终通过调用构造函数来创建它们：

    • 创建空实例： bytearray()

    • 创建具有给定长度的 0 填充实例： bytearray(10)

    • 来自整数迭代： bytearray(range(20))

    • 凭借缓冲协议拷贝现有二进制数据： bytearray(b'Hi!')

    由于 bytearray 对象是可变的，它们支持 可变 序列操作，除了常见 bytes 和 bytearray 的操作描述在 bytes 和 bytearray 操作 .

    另请参阅 bytearray 内置。

    Since 2 hexadecimal digits correspond precisely to a single byte, hexadecimal numbers are a commonly used format for describing binary data. Accordingly, the bytearray type has an additional class method to read data in that format:

    classmethod fromhex ( string ) ¶

    This bytearray class method returns bytearray object, decoding the given string object. The string must contain two hexadecimal digits per byte, with ASCII whitespace being ignored. 

    >>> bytearray.fromhex('2Ef0 F1f2  ')
bytearray(b'.\xf0\xf1\xf2')

    3.7 版改变： bytearray.fromhex() 现在跳过字符串中的所有 ASCII 空白，不仅仅空格。

    A reverse conversion function exists to transform a bytearray object into its hexadecimal representation.

    hex ( [ sep [ , bytes_per_sep ] ] ) ¶

    返回字符串对象，实例包含每字节 2 十六进制数字。 

    >>> bytearray(b'\xf0\xf1\xf2').hex()
'f0f1f2'

    Added in version 3.5.

    3.8 版改变： 类似于 bytes.hex() , bytearray.hex() 现在支持可选 sep and bytes_per_sep 参数以在十六进制输出的字节之间插入分隔符。

    Since bytearray objects are sequences of integers (akin to a list), for a bytearray object b , b[0] 将是整数，而 b[0:1] will be a bytearray object of length 1. (This contrasts with text strings, where both indexing and slicing will produce a string of length 1)

    The representation of bytearray objects uses the bytes literal format ( bytearray(b'...') ) 因为它通常更有用，比如 bytearray([46, 46, 46]) . You can always convert a bytearray object into a list of integers using list(b) .

    bytes 和 bytearray 操作 ¶

    bytes 和 bytearray 对象两者支持 common sequence operations. They interoperate not just with operands of the same type, but with any 像字节对象 . Due to this flexibility, they can be freely mixed in operations without causing errors. However, the return type of the result may depend on the order of operands.

    注意

    The methods on bytes and bytearray objects don’t accept strings as their arguments, just as the methods on strings don’t accept bytes as their arguments. For example, you have to write: 

    a = "abc"
b = a.replace("a", "f")

    and: 

    a = b"abc"
b = a.replace(b"a", b"f")

    Some bytes and bytearray operations assume the use of ASCII compatible binary formats, and hence should be avoided when working with arbitrary binary data. These restrictions are covered below.

    注意

    Using these ASCII based operations to manipulate binary data that is not stored in an ASCII based format may lead to data corruption.

    The following methods on bytes and bytearray objects can be used with arbitrary binary data.

    字节。 count ( sub [ , start [ , end ] ] ) ¶
    bytearray. count ( sub [ , start [ , end ] ] ) ¶

    Return the number of non-overlapping occurrences of subsequence sub 在范围 [ start , end ]。可选自变量 start and end 按切片表示法解释。

    要搜索的子序列可以是任何 像字节对象 或 0 到 255 范围内的整数。

    若 sub is empty, returns the number of empty slices between characters which is the length of the bytes object plus one.

    3.3 版改变： 还接受 0 到 255 范围内的整数作为子序列。

    字节。 removeprefix ( prefix , / ) ¶
    bytearray. removeprefix ( prefix , / ) ¶

    若二进制数据开始采用 prefix 字符串，返回 bytes[len(prefix):] 。否则，返回原始二进制数据副本： 

    >>> b'TestHook'.removeprefix(b'Test')
b'Hook'
>>> b'BaseTestCase'.removeprefix(b'Test')
b'BaseTestCase'

    The prefix 可以是任何 像字节对象 .

    注意

    The bytearray version of this method does not operate in place - it always produces a new object, even if no changes were made.

    Added in version 3.9.

    字节。 removesuffix ( suffix , / ) ¶
    bytearray. removesuffix ( suffix , / ) ¶

    若二进制数据结束采用 suffix 字符串和 suffix 不为空，返回 bytes[:-len(suffix)] 。否则，返回原始二进制数据副本： 

    >>> b'MiscTests'.removesuffix(b'Tests')
b'Misc'
>>> b'TmpDirMixin'.removesuffix(b'Tests')
b'TmpDirMixin'

    The suffix 可以是任何 像字节对象 .

    注意

    The bytearray version of this method does not operate in place - it always produces a new object, even if no changes were made.

    Added in version 3.9.

    字节。 decode ( encoding = 'utf-8' , errors = 'strict' ) ¶
    bytearray. decode ( encoding = 'utf-8' , errors = 'strict' ) ¶

    Return the bytes decoded to a str .

    encoding 默认为 'utf-8' ；见 标准编码 了解可能值。

    errors controls how decoding errors are handled. If 'strict' (默认)， UnicodeError exception is raised. Other possible values are 'ignore' , 'replace' , and any other name registered via codecs.register_error() 。见 错误处理程序 了解细节。

    For performance reasons, the value of errors is not checked for validity unless a decoding error actually occurs, Python 开发模式 is enabled or a 调试构建 被使用。

    注意

    传递 encoding 自变量对于 str 允许解码任何 像字节对象 directly, without needing to make a temporary bytes or bytearray 对象。

    3.1 版改变： 添加支持关键词自变量。

    3.9 版改变： 值对于 errors argument is now checked in Python 开发模式 和在 调试模式 .

    字节。 endswith ( suffix [ , start [ , end ] ] ) ¶
    bytearray. endswith ( suffix [ , start [ , end ] ] ) ¶

    返回 True if the binary data ends with the specified suffix ，否则返回 False . suffix can also be a tuple of suffixes to look for. With optional start , test beginning at that position. With optional end , stop comparing at that position.

    The suffix(es) to search for may be any 像字节对象 .

    字节。 find ( sub [ , start [ , end ] ] ) ¶
    bytearray. find ( sub [ , start [ , end ] ] ) ¶

    Return the lowest index in the data where the subsequence sub 被发现，这种 sub is contained in the slice s[start:end] 。可选自变量 start and end 按切片表示法解释。返回 -1 if sub 找不到。

    要搜索的子序列可以是任何 像字节对象 或 0 到 255 范围内的整数。

    注意

    The find() 方法才应被使用，若需要知道位置为 sub 。要校验若 sub 是子字符串或不是，使用 in 运算符： 

    >>> b'Py' in b'Python'
True

    3.3 版改变： 还接受 0 到 255 范围内的整数作为子序列。

    字节。 index ( sub [ , start [ , end ] ] ) ¶
    bytearray. index ( sub [ , start [ , end ] ] ) ¶

    像 find() ，但会引发 ValueError 当找不到子序列时。

    要搜索的子序列可以是任何 像字节对象 或 0 到 255 范围内的整数。

    3.3 版改变： 还接受 0 到 255 范围内的整数作为子序列。

    字节。 join ( iterable ) ¶
    bytearray. join ( iterable ) ¶

    Return a bytes or bytearray object which is the concatenation of the binary data sequences in iterable 。 TypeError will be raised if there are any values in iterable that are not 像字节对象 ，包括 str objects. The separator between elements is the contents of the bytes or bytearray object providing this method.

    static 字节。 maketrans ( from , to ) ¶
    static bytearray. maketrans ( from , to ) ¶

    此静态方法返回的翻译表可用于 bytes.translate() that will map each character in from into the character at the same position in to ; from and to must both be 像字节对象 and have the same length.

    Added in version 3.1.

    字节。 partition ( sep ) ¶
    bytearray. partition ( sep ) ¶

    Split the sequence at the first occurrence of sep , and return a 3-tuple containing the part before the separator, the separator itself or its bytearray copy, and the part after the separator. If the separator is not found, return a 3-tuple containing a copy of the original sequence, followed by two empty bytes or bytearray objects.

    The separator to search for may be any 像字节对象 .

    字节。 replace ( old , new [ , count ] ) ¶
    bytearray. replace ( old , new [ , count ] ) ¶

    Return a copy of the sequence with all occurrences of subsequence old 被替换通过 new 。若可选自变量 count 有给定，仅前 count 出现被替换。

    The subsequence to search for and its replacement may be any 像字节对象 .

    注意

    The bytearray version of this method does not operate in place - it always produces a new object, even if no changes were made.

    字节。 rfind ( sub [ , start [ , end ] ] ) ¶
    bytearray. rfind ( sub [ , start [ , end ] ] ) ¶

    Return the highest index in the sequence where the subsequence sub 被发现，这种 sub 包含在 s[start:end] 。可选自变量 start and end 按切片表示法解释。返回 -1 当故障时。

    要搜索的子序列可以是任何 像字节对象 或 0 到 255 范围内的整数。

    3.3 版改变： 还接受 0 到 255 范围内的整数作为子序列。

    字节。 rindex ( sub [ , start [ , end ] ] ) ¶
    bytearray. rindex ( sub [ , start [ , end ] ] ) ¶

    像 rfind() 但引发 ValueError 当子序列 sub 找不到。

    要搜索的子序列可以是任何 像字节对象 或 0 到 255 范围内的整数。

    3.3 版改变： 还接受 0 到 255 范围内的整数作为子序列。

    字节。 rpartition ( sep ) ¶
    bytearray. rpartition ( sep ) ¶

    Split the sequence at the last occurrence of sep , and return a 3-tuple containing the part before the separator, the separator itself or its bytearray copy, and the part after the separator. If the separator is not found, return a 3-tuple containing two empty bytes or bytearray objects, followed by a copy of the original sequence.

    The separator to search for may be any 像字节对象 .

    字节。 startswith ( prefix [ , start [ , end ] ] ) ¶
    bytearray. startswith ( prefix [ , start [ , end ] ] ) ¶

    返回 True if the binary data starts with the specified prefix ，否则返回 False . prefix can also be a tuple of prefixes to look for. With optional start , test beginning at that position. With optional end , stop comparing at that position.

    The prefix(es) to search for may be any 像字节对象 .

    字节。 translate ( table , / , delete = b'' ) ¶
    bytearray. translate ( table , / , delete = b'' ) ¶

    Return a copy of the bytes or bytearray object where all bytes occurring in the optional argument delete are removed, and the remaining bytes have been mapped through the given translation table, which must be a bytes object of length 256.

    可以使用 bytes.maketrans() method to create a translation table.

    设置 table 自变量对于 None for translations that only delete characters: 

    >>> b'read this short text'.translate(None, b'aeiou')
b'rd ths shrt txt'

    3.6 版改变： delete is now supported as a keyword argument.

    The following methods on bytes and bytearray objects have default behaviours that assume the use of ASCII compatible binary formats, but can still be used with arbitrary binary data by passing appropriate arguments. Note that all of the bytearray methods in this section do not operate in place, and instead produce new objects.

    字节。 center ( width [ , fillbyte ] ) ¶
    bytearray. center ( width [ , fillbyte ] ) ¶

    Return a copy of the object centered in a sequence of length width 。铺垫的履行是使用指定 fillbyte (default is an ASCII space). For bytes objects, the original sequence is returned if width <= len(s) .

    注意

    The bytearray version of this method does not operate in place - it always produces a new object, even if no changes were made.

    字节。 ljust ( width [ , fillbyte ] ) ¶
    bytearray. ljust ( width [ , fillbyte ] ) ¶

    Return a copy of the object left justified in a sequence of length width 。铺垫的履行是使用指定 fillbyte (default is an ASCII space). For bytes objects, the original sequence is returned if width <= len(s) .

    注意

    The bytearray version of this method does not operate in place - it always produces a new object, even if no changes were made.

    字节。 lstrip ( [ chars ] ) ¶
    bytearray. lstrip ( [ chars ] ) ¶

    Return a copy of the sequence with specified leading bytes removed. The chars argument is a binary sequence specifying the set of byte values to be removed - the name refers to the fact this method is usually used with ASCII characters. If omitted or None ， chars argument defaults to removing ASCII whitespace. The chars 自变量不是前缀；在一定程度上，会剥离其值的所有组合： 

    >>> b'   spacious   '.lstrip()
b'spacious   '
>>> b'www.example.com'.lstrip(b'cmowz.')
b'example.com'

    要移除的字节值二进制序列可以是任何 像字节对象 。见 removeprefix() for a method that will remove a single prefix string rather than all of a set of characters. For example: 

    >>> b'Arthur: three!'.lstrip(b'Arthur: ')
b'ee!'
>>> b'Arthur: three!'.removeprefix(b'Arthur: ')
b'three!'

    注意

    The bytearray version of this method does not operate in place - it always produces a new object, even if no changes were made.

    字节。 rjust ( width [ , fillbyte ] ) ¶
    bytearray. rjust ( width [ , fillbyte ] ) ¶

    Return a copy of the object right justified in a sequence of length width 。铺垫的履行是使用指定 fillbyte (default is an ASCII space). For bytes objects, the original sequence is returned if width <= len(s) .

    注意

    The bytearray version of this method does not operate in place - it always produces a new object, even if no changes were made.

    字节。 rsplit ( sep = None , maxsplit = -1 ) ¶
    bytearray. rsplit ( sep = None , maxsplit = -1 ) ¶

    Split the binary sequence into subsequences of the same type, using sep 作为定界符字符串。若 maxsplit is given, at most maxsplit splits are done, the rightmost ones. If sep 未指定或 None , any subsequence consisting solely of ASCII whitespace is a separator. Except for splitting from the right, rsplit() behaves like split() which is described in detail below.

    字节。 rstrip ( [ chars ] ) ¶
    bytearray. rstrip ( [ chars ] ) ¶

    Return a copy of the sequence with specified trailing bytes removed. The chars argument is a binary sequence specifying the set of byte values to be removed - the name refers to the fact this method is usually used with ASCII characters. If omitted or None ， chars argument defaults to removing ASCII whitespace. The chars 自变量不是后缀；在一定程度上，会剥离其值的所有组合： 

    >>> b'   spacious   '.rstrip()
b'   spacious'
>>> b'mississippi'.rstrip(b'ipz')
b'mississ'

    要移除的字节值二进制序列可以是任何 像字节对象 。见 removesuffix() for a method that will remove a single suffix string rather than all of a set of characters. For example: 

    >>> b'Monty Python'.rstrip(b' Python')
b'M'
>>> b'Monty Python'.removesuffix(b' Python')
b'Monty'

    注意

    The bytearray version of this method does not operate in place - it always produces a new object, even if no changes were made.

    字节。 split ( sep = None , maxsplit = -1 ) ¶
    bytearray. split ( sep = None , maxsplit = -1 ) ¶

    Split the binary sequence into subsequences of the same type, using sep 作为定界符字符串。若 maxsplit is given and non-negative, at most maxsplit splits are done (thus, the list will have at most maxsplit+1 elements). If maxsplit 未指定或是 -1 , then there is no limit on the number of splits (all possible splits are made).

    若 sep is given, consecutive delimiters are not grouped together and are deemed to delimit empty subsequences (for example, b'1,,2'.split(b',') 返回 [b'1', b'', b'2'] )。 sep argument may consist of a multibyte sequence (for example, b'1<>2<>3'.split(b'<>') 返回 [b'1', b'2', b'3'] ). Splitting an empty sequence with a specified separator returns [b''] or [bytearray(b'')] depending on the type of object being split. The sep 自变量可以是任何 像字节对象 .

    例如： 

    >>> b'1,2,3'.split(b',')
[b'1', b'2', b'3']
>>> b'1,2,3'.split(b',', maxsplit=1)
[b'1', b'2,3']
>>> b'1,2,,3,'.split(b',')
[b'1', b'2', b'', b'3', b'']

    若 sep 未指定或是 None , a different splitting algorithm is applied: runs of consecutive ASCII whitespace are regarded as a single separator, and the result will contain no empty strings at the start or end if the sequence has leading or trailing whitespace. Consequently, splitting an empty sequence or a sequence consisting solely of ASCII whitespace without a specified separator returns [] .

    例如： 

    >>> b'1 2 3'.split()
[b'1', b'2', b'3']
>>> b'1 2 3'.split(maxsplit=1)
[b'1', b'2 3']
>>> b'   1   2   3   '.split()
[b'1', b'2', b'3']
    字节。 strip ( [ chars ] ) ¶
    bytearray. strip ( [ chars ] ) ¶

    Return a copy of the sequence with specified leading and trailing bytes removed. The chars argument is a binary sequence specifying the set of byte values to be removed - the name refers to the fact this method is usually used with ASCII characters. If omitted or None ， chars argument defaults to removing ASCII whitespace. The chars 自变量不是前缀 (或后缀)；在一定程度上，会剥离其值的所有组合： 

    >>> b'   spacious   '.strip()
b'spacious'
>>> b'www.example.com'.strip(b'cmowz.')
b'example'

    要移除的字节值二进制序列可以是任何 像字节对象 .

    注意

    The bytearray version of this method does not operate in place - it always produces a new object, even if no changes were made.

    The following methods on bytes and bytearray objects assume the use of ASCII compatible binary formats and should not be applied to arbitrary binary data. Note that all of the bytearray methods in this section do not operate in place, and instead produce new objects.

    字节。 capitalize ( ) ¶
    bytearray. capitalize ( ) ¶

    Return a copy of the sequence with each byte interpreted as an ASCII character, and the first byte capitalized and the rest lowercased. Non-ASCII byte values are passed through unchanged.

    注意

    The bytearray version of this method does not operate in place - it always produces a new object, even if no changes were made.

    字节。 expandtabs ( tabsize = 8 ) ¶
    bytearray. expandtabs ( tabsize = 8 ) ¶

    Return a copy of the sequence where all ASCII tab characters are replaced by one or more ASCII spaces, depending on the current column and the given tab size. Tab positions occur every tabsize bytes (default is 8, giving tab positions at columns 0, 8, 16 and so on). To expand the sequence, the current column is set to zero and the sequence is examined byte by byte. If the byte is an ASCII tab character ( b'\t' ), one or more space characters are inserted in the result until the current column is equal to the next tab position. (The tab character itself is not copied.) If the current byte is an ASCII newline ( b'\n' ) or carriage return ( b'\r' ), it is copied and the current column is reset to zero. Any other byte value is copied unchanged and the current column is incremented by one regardless of how the byte value is represented when printed: 

    >>> b'01\t012\t0123\t01234'.expandtabs()
b'01      012     0123    01234'
>>> b'01\t012\t0123\t01234'.expandtabs(4)
b'01  012 0123    01234'

    注意

    The bytearray version of this method does not operate in place - it always produces a new object, even if no changes were made.

    字节。 isalnum ( ) ¶
    bytearray. isalnum ( ) ¶

    返回 True if all bytes in the sequence are alphabetical ASCII characters or ASCII decimal digits and the sequence is not empty, False otherwise. Alphabetic ASCII characters are those byte values in the sequence b'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ' . ASCII decimal digits are those byte values in the sequence b'0123456789' .

    例如： 

    >>> b'ABCabc1'.isalnum()
True
>>> b'ABC abc1'.isalnum()
False
    字节。 isalpha ( ) ¶
    bytearray. isalpha ( ) ¶

    返回 True if all bytes in the sequence are alphabetic ASCII characters and the sequence is not empty, False otherwise. Alphabetic ASCII characters are those byte values in the sequence b'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ' .

    例如： 

    >>> b'ABCabc'.isalpha()
True
>>> b'ABCabc1'.isalpha()
False
    字节。 isascii ( ) ¶
    bytearray. isascii ( ) ¶

    返回 True 若序列为空 (或序列中的所有 bytes 都是 ASCII)， False 否则。ASCII 字节在范围 0-0x7F。

    Added in version 3.7.

    字节。 isdigit ( ) ¶
    bytearray. isdigit ( ) ¶

    返回 True if all bytes in the sequence are ASCII decimal digits and the sequence is not empty, False otherwise. ASCII decimal digits are those byte values in the sequence b'0123456789' .

    例如： 

    >>> b'1234'.isdigit()
True
>>> b'1.23'.isdigit()
False
    字节。 islower ( ) ¶
    bytearray. islower ( ) ¶

    返回 True if there is at least one lowercase ASCII character in the sequence and no uppercase ASCII characters, False 否则。

    例如： 

    >>> b'hello world'.islower()
True
>>> b'Hello world'.islower()
False

    Lowercase ASCII characters are those byte values in the sequence b'abcdefghijklmnopqrstuvwxyz' . Uppercase ASCII characters are those byte values in the sequence b'ABCDEFGHIJKLMNOPQRSTUVWXYZ' .

    字节。 isspace ( ) ¶
    bytearray. isspace ( ) ¶

    返回 True if all bytes in the sequence are ASCII whitespace and the sequence is not empty, False otherwise. ASCII whitespace characters are those byte values in the sequence b' \t\n\r\x0b\f' (space, tab, newline, carriage return, vertical tab, form feed).

    字节。 istitle ( ) ¶
    bytearray. istitle ( ) ¶

    返回 True if the sequence is ASCII titlecase and the sequence is not empty, False otherwise. See bytes.title() for more details on the definition of “titlecase”.

    例如： 

    >>> b'Hello World'.istitle()
True
>>> b'Hello world'.istitle()
False
    字节。 isupper ( ) ¶
    bytearray. isupper ( ) ¶

    返回 True if there is at least one uppercase alphabetic ASCII character in the sequence and no lowercase ASCII characters, False 否则。

    例如： 

    >>> b'HELLO WORLD'.isupper()
True
>>> b'Hello world'.isupper()
False

    Lowercase ASCII characters are those byte values in the sequence b'abcdefghijklmnopqrstuvwxyz' . Uppercase ASCII characters are those byte values in the sequence b'ABCDEFGHIJKLMNOPQRSTUVWXYZ' .

    字节。 lower ( ) ¶
    bytearray. lower ( ) ¶

    Return a copy of the sequence with all the uppercase ASCII characters converted to their corresponding lowercase counterpart.

    例如： 

    >>> b'Hello World'.lower()
b'hello world'

    Lowercase ASCII characters are those byte values in the sequence b'abcdefghijklmnopqrstuvwxyz' . Uppercase ASCII characters are those byte values in the sequence b'ABCDEFGHIJKLMNOPQRSTUVWXYZ' .

    注意

    The bytearray version of this method does not operate in place - it always produces a new object, even if no changes were made.

    字节。 splitlines ( keepends = False ) ¶
    bytearray. splitlines ( keepends = False ) ¶

    Return a list of the lines in the binary sequence, breaking at ASCII line boundaries. This method uses the 通用换行符 approach to splitting lines. Line breaks are not included in the resulting list unless keepends is given and true.

    例如： 

    >>> b'ab c\n\nde fg\rkl\r\n'.splitlines()
[b'ab c', b'', b'de fg', b'kl']
>>> b'ab c\n\nde fg\rkl\r\n'.splitlines(keepends=True)
[b'ab c\n', b'\n', b'de fg\r', b'kl\r\n']

    不像 split() when a delimiter string sep is given, this method returns an empty list for the empty string, and a terminal line break does not result in an extra line: 

    >>> b"".split(b'\n'), b"Two lines\n".split(b'\n')
([b''], [b'Two lines', b''])
>>> b"".splitlines(), b"One line\n".splitlines()
([], [b'One line'])
    字节。 swapcase ( ) ¶
    bytearray. swapcase ( ) ¶

    Return a copy of the sequence with all the lowercase ASCII characters converted to their corresponding uppercase counterpart and vice-versa.

    例如： 

    >>> b'Hello World'.swapcase()
b'hELLO wORLD'

    Lowercase ASCII characters are those byte values in the sequence b'abcdefghijklmnopqrstuvwxyz' . Uppercase ASCII characters are those byte values in the sequence b'ABCDEFGHIJKLMNOPQRSTUVWXYZ' .

    不像 str.swapcase() , it is always the case that bin.swapcase().swapcase() == bin for the binary versions. Case conversions are symmetrical in ASCII, even though that is not generally true for arbitrary Unicode code points.

    注意

    The bytearray version of this method does not operate in place - it always produces a new object, even if no changes were made.

    字节。 title ( ) ¶
    bytearray. title ( ) ¶

    Return a titlecased version of the binary sequence where words start with an uppercase ASCII character and the remaining characters are lowercase. Uncased byte values are left unmodified.

    例如： 

    >>> b'Hello world'.title()
b'Hello World'

    Lowercase ASCII characters are those byte values in the sequence b'abcdefghijklmnopqrstuvwxyz' . Uppercase ASCII characters are those byte values in the sequence b'ABCDEFGHIJKLMNOPQRSTUVWXYZ' . All other byte values are uncased.

    The algorithm uses a simple language-independent definition of a word as groups of consecutive letters. The definition works in many contexts but it means that apostrophes in contractions and possessives form word boundaries, which may not be the desired result: 

    >>> b"they're bill's friends from the UK".title()
b"They'Re Bill'S Friends From The Uk"

    A workaround for apostrophes can be constructed using regular expressions: 

    >>> import re
>>> def titlecase(s):
...     return re.sub(rb"[A-Za-z]+('[A-Za-z]+)?",
...                   lambda mo: mo.group(0)[0:1].upper() +
...                              mo.group(0)[1:].lower(),
...                   s)
...
>>> titlecase(b"they're bill's friends.")
b"They're Bill's Friends."

    注意

    The bytearray version of this method does not operate in place - it always produces a new object, even if no changes were made.

    字节。 upper ( ) ¶
    bytearray. upper ( ) ¶

    Return a copy of the sequence with all the lowercase ASCII characters converted to their corresponding uppercase counterpart.

    例如： 

    >>> b'Hello World'.upper()
b'HELLO WORLD'

    Lowercase ASCII characters are those byte values in the sequence b'abcdefghijklmnopqrstuvwxyz' . Uppercase ASCII characters are those byte values in the sequence b'ABCDEFGHIJKLMNOPQRSTUVWXYZ' .

    注意

    The bytearray version of this method does not operate in place - it always produces a new object, even if no changes were made.

    字节。 zfill ( width ) ¶
    bytearray. zfill ( width ) ¶

    Return a copy of the sequence left filled with ASCII b'0' digits to make a sequence of length width . A leading sign prefix ( b'+' / b'-' ) is handled by inserting the padding after the sign character rather than before. For bytes objects, the original sequence is returned if width <= len(seq) .

    例如： 

    >>> b"42".zfill(5)
b'00042'
>>> b"-42".zfill(5)
b'-0042'

    注意

    The bytearray version of this method does not operate in place - it always produces a new object, even if no changes were made.

    printf 样式字节格式化 ¶

    注意

    The formatting operations described here exhibit a variety of quirks that lead to a number of common errors (such as failing to display tuples and dictionaries correctly). If the value being printed may be a tuple or dictionary, wrap it in a tuple.

    Bytes objects ( bytes / bytearray ) have one unique built-in operation: the % operator (modulo). This is also known as the bytes formatting or interpolation operator. Given format % values (在哪里 format is a bytes object), % conversion specifications in format are replaced with zero or more elements of 值 . The effect is similar to using the sprintf() 在 C 语言中。

    若 format requires a single argument, 值 may be a single non-tuple object. [ 5 ] 否则， 值 must be a tuple with exactly the number of items specified by the format bytes object, or a single mapping object (for example, a dictionary).

    A conversion specifier contains two or more characters and has the following components, which must occur in this order:

    1. The '%' character, which marks the start of the specifier.

    2. Mapping key (optional), consisting of a parenthesised sequence of characters (for example, (somename) ).

    3. Conversion flags (optional), which affect the result of some conversion types.

    4. Minimum field width (optional). If specified as an '*' (asterisk), the actual width is read from the next element of the tuple in 值 , and the object to convert comes after the minimum field width and optional precision.

    5. Precision (optional), given as a '.' (dot) followed by the precision. If specified as '*' (an asterisk), the actual precision is read from the next element of the tuple in 值 , and the value to convert comes after the precision.

    6. Length modifier (optional).

    7. 转换类型。

    When the right argument is a dictionary (or other mapping type), then the formats in the bytes object must include a parenthesised mapping key into that dictionary inserted immediately after the '%' character. The mapping key selects the value to be formatted from the mapping. For example: 

    >>> print(b'%(language)s has %(number)03d quote types.' %
...       {b'language': b"Python", b"number": 2})
b'Python has 002 quote types.'

    In this case no * specifiers may occur in a format (since they require a sequential parameter list).

    转换标志字符：

    标志

    含义

    '#'

    The value conversion will use the “alternate form” (where defined below).

    '0'

    		The conversion will be zero padded for numeric values.

    '-'

    The converted value is left adjusted (overrides the '0' conversion if both are given).

    ' '

    (a space) A blank should be left before a positive number (or empty string) produced by a signed conversion.

    '+'

    A sign character ( '+' or '-' ) will precede the conversion (overrides a “space” flag).

    A length modifier ( h , l ，或 L ) may be present, but is ignored as it is not necessary for Python – so e.g. %ld is identical to %d .

    转换类型：

    转换

    含义

    注意事项

    'd'

    		有符号整数十进制。

    'i'

    		有符号整数十进制。

    'o'

    		有符号八进制值。 (1)

    'u'

    过时 type – 它等同于 'd' .

    		(8)

    'x'

    		有符号十六进制 (小写)。 (2)

    'X'

    		有符号十六进制 (大写)。 (2)

    'e'

    		浮点指数格式 (小写)。 (3)

    'E'

    		浮点指数格式 (大写)。 (3)

    'f'

    		浮点十进制格式。 (3)

    'F'

    		浮点十进制格式。 (3)

    'g'

    Floating point format. Uses lowercase exponential format if exponent is less than -4 or not less than precision, decimal format otherwise.

    		(4)

    'G'

    Floating point format. Uses uppercase exponential format if exponent is less than -4 or not less than precision, decimal format otherwise.

    		(4)

    'c'

    单字节 (接受整数或单字节对象)。

    'b'

    Bytes (any object that follows the 缓冲协议 or has __bytes__() ).

    		(5)

    's'

    's' 是别名化的 'b' and should only be used for Python2/3 code bases.

    		(6)

    'a'

    Bytes (converts any Python object using repr(obj).encode('ascii', 'backslashreplace') ).

    		(5)

    'r'

    'r' 是别名化的 'a' and should only be used for Python2/3 code bases.

    		(7)

    '%'

    No argument is converted, results in a '%' character in the result.

    注意事项：

    1. The alternate form causes a leading octal specifier ( '0o' ) to be inserted before the first digit.

    2. The alternate form causes a leading '0x' or '0X' (depending on whether the 'x' or 'X' format was used) to be inserted before the first digit.

    3. The alternate form causes the result to always contain a decimal point, even if no digits follow it.

      The precision determines the number of digits after the decimal point and defaults to 6.

    4. The alternate form causes the result to always contain a decimal point, and trailing zeroes are not removed as they would otherwise be.

      The precision determines the number of significant digits before and after the decimal point and defaults to 6.

    5. 若精度为 N ，会截取输出成 N 字符。

    6. b'%s' is deprecated, but will not be removed during the 3.x series.

    7. b'%r' is deprecated, but will not be removed during the 3.x series.

    8. 见 PEP 237 .

    注意

    The bytearray version of this method does not operate in place - it always produces a new object, even if no changes were made.

    另请参阅

    PEP 461 - 为 bytes 和 bytearray 添加 % 格式化

    Added in version 3.5.

    内存视图 ¶

    memoryview objects allow Python code to access the internal data of an object that supports the 缓冲协议 without copying.

    class memoryview ( object ) ¶

    创建 memoryview that references object . object must support the buffer protocol. Built-in objects that support the buffer protocol include bytes and bytearray .

    A memoryview has the notion of an element , which is the atomic memory unit handled by the originating object . For many simple types such as bytes and bytearray , an element is a single byte, but other types such as array.array may have bigger elements.

    len(view) is equal to the length of tolist , which is the nested list representation of the view. If view.ndim = 1 , this is equal to the number of elements in the view.

    Changed in version 3.12: 若 view.ndim == 0 , len(view) 现在引发 TypeError instead of returning 1.

    The itemsize attribute will give you the number of bytes in a single element.

    A memoryview supports slicing and indexing to expose its data. One-dimensional slicing will result in a subview: 

    >>> v = memoryview(b'abcefg')
>>> v[1]
98
>>> v[-1]
103
>>> v[1:4]
<memory at 0x7f3ddc9f4350>
>>> bytes(v[1:4])
b'bce'

    若 format is one of the native format specifiers from the struct module, indexing with an integer or a tuple of integers is also supported and returns a single element with the correct type. One-dimensional memoryviews can be indexed with an integer or a one-integer tuple. Multi-dimensional memoryviews can be indexed with tuples of exactly ndim integers where ndim is the number of dimensions. Zero-dimensional memoryviews can be indexed with the empty tuple.

    Here is an example with a non-byte format: 

    >>> import array
>>> a = array.array('l', [-11111111, 22222222, -33333333, 44444444])
>>> m = memoryview(a)
>>> m[0]
-11111111
>>> m[-1]
44444444
>>> m[::2].tolist()
[-11111111, -33333333]

    If the underlying object is writable, the memoryview supports one-dimensional slice assignment. Resizing is not allowed: 

    >>> data = bytearray(b'abcefg')
>>> v = memoryview(data)
>>> v.readonly
False
>>> v[0] = ord(b'z')
>>> data
bytearray(b'zbcefg')
>>> v[1:4] = b'123'
>>> data
bytearray(b'z123fg')
>>> v[2:3] = b'spam'
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: memoryview assignment: lvalue and rvalue have different structures
>>> v[2:6] = b'spam'
>>> data
bytearray(b'z1spam')

    One-dimensional memoryviews of hashable (read-only) types with formats ‘B’, ‘b’ or ‘c’ are also hashable. The hash is defined as hash(m) == hash(m.tobytes()) : 

    >>> v = memoryview(b'abcefg')
>>> hash(v) == hash(b'abcefg')
True
>>> hash(v[2:4]) == hash(b'ce')
True
>>> hash(v[::-2]) == hash(b'abcefg'[::-2])
True

    3.3 版改变： One-dimensional memoryviews can now be sliced. One-dimensional memoryviews with formats ‘B’, ‘b’ or ‘c’ are now hashable .

    3.4 版改变： memoryview is now registered automatically with collections.abc.Sequence

    3.5 版改变： memoryviews can now be indexed with tuple of integers.

    memoryview 有几个方法：

    __eq__ ( exporter ) ¶

    A memoryview and a PEP 3118 exporter are equal if their shapes are equivalent and if all corresponding values are equal when the operands’ respective format codes are interpreted using struct 句法。

    For the subset of struct format strings currently supported by tolist() , v and w are equal if v.tolist() == w.tolist() : 

    >>> import array
>>> a = array.array('I', [1, 2, 3, 4, 5])
>>> b = array.array('d', [1.0, 2.0, 3.0, 4.0, 5.0])
>>> c = array.array('b', [5, 3, 1])
>>> x = memoryview(a)
>>> y = memoryview(b)
>>> x == a == y == b
True
>>> x.tolist() == a.tolist() == y.tolist() == b.tolist()
True
>>> z = y[::-2]
>>> z == c
True
>>> z.tolist() == c.tolist()
True

    If either format string is not supported by the struct module, then the objects will always compare as unequal (even if the format strings and buffer contents are identical): 

    >>> from ctypes import BigEndianStructure, c_long
>>> class BEPoint(BigEndianStructure):
...     _fields_ = [("x", c_long), ("y", c_long)]
...
>>> point = BEPoint(100, 200)
>>> a = memoryview(point)
>>> b = memoryview(point)
>>> a == point
False
>>> a == b
False

    Note that, as with floating point numbers, v is w does not imply v == w 对于 memoryview 对象。

    3.3 版改变： Previous versions compared the raw memory disregarding the item format and the logical array structure.

    tobytes ( order = 'C' ) ¶

    Return the data in the buffer as a bytestring. This is equivalent to calling the bytes constructor on the memoryview. 

    >>> m = memoryview(b"abc")
>>> m.tobytes()
b'abc'
>>> bytes(m)
b'abc'

    For non-contiguous arrays the result is equal to the flattened list representation with all elements converted to bytes. tobytes() supports all format strings, including those that are not in struct module syntax.

    Added in version 3.8: order can be {‘C’, ‘F’, ‘A’}. When order is ‘C’ or ‘F’, the data of the original array is converted to C or Fortran order. For contiguous views, ‘A’ returns an exact copy of the physical memory. In particular, in-memory Fortran order is preserved. For non-contiguous views, the data is converted to C first. order=None 如同 order=’C’ .

    hex ( [ sep [ , bytes_per_sep ] ] ) ¶

    Return a string object containing two hexadecimal digits for each byte in the buffer. 

    >>> m = memoryview(b"abc")
>>> m.hex()
'616263'

    Added in version 3.5.

    3.8 版改变： 类似于 bytes.hex() , memoryview.hex() 现在支持可选 sep and bytes_per_sep 参数以在十六进制输出的字节之间插入分隔符。

    tolist ( ) ¶

    Return the data in the buffer as a list of elements. 

    >>> memoryview(b'abc').tolist()
[97, 98, 99]
>>> import array
>>> a = array.array('d', [1.1, 2.2, 3.3])
>>> m = memoryview(a)
>>> m.tolist()
[1.1, 2.2, 3.3]

    3.3 版改变： tolist() now supports all single character native formats in struct module syntax as well as multi-dimensional representations.

    toreadonly ( ) ¶

    Return a readonly version of the memoryview object. The original memoryview object is unchanged. 

    >>> m = memoryview(bytearray(b'abc'))
>>> mm = m.toreadonly()
>>> mm.tolist()
[97, 98, 99]
>>> mm[0] = 42
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: cannot modify read-only memory
>>> m[0] = 43
>>> mm.tolist()
[43, 98, 99]

    Added in version 3.8.

    release ( ) ¶

    Release the underlying buffer exposed by the memoryview object. Many objects take special actions when a view is held on them (for example, a bytearray would temporarily forbid resizing); therefore, calling release() is handy to remove these restrictions (and free any dangling resources) as soon as possible.

    After this method has been called, any further operation on the view raises a ValueError (except release() itself which can be called multiple times): 

    >>> m = memoryview(b'abc')
>>> m.release()
>>> m[0]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: operation forbidden on released memoryview object

    The context management protocol can be used for a similar effect, using the with 语句： 

    >>> with memoryview(b'abc') as m:
...     m[0]
...
97
>>> m[0]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: operation forbidden on released memoryview object

    Added in version 3.2.

    cast ( format [ , shape ] ) ¶

    将 memoryview 铸造成新格式 (或新形状)。 shape 默认为 [byte_length//new_itemsize] , which means that the result view will be one-dimensional. The return value is a new memoryview, but the buffer itself is not copied. Supported casts are 1D -> C- contiguous and C-contiguous -> 1D.

    The destination format is restricted to a single element native format in struct syntax. One of the formats must be a byte format (‘B’, ‘b’ or ‘c’). The byte length of the result must be the same as the original length. Note that all byte lengths may depend on the operating system.

    铸造 1D/long 成 1D/无符号 bytes： 

    >>> import array
>>> a = array.array('l', [1,2,3])
>>> x = memoryview(a)
>>> x.format
'l'
>>> x.itemsize
8
>>> len(x)
3
>>> x.nbytes
24
>>> y = x.cast('B')
>>> y.format
'B'
>>> y.itemsize
1
>>> len(y)
24
>>> y.nbytes
24

    Cast 1D/unsigned bytes to 1D/char: 

    >>> b = bytearray(b'zyz')
>>> x = memoryview(b)
>>> x[0] = b'a'
Traceback (most recent call last):
  ...
TypeError: memoryview: invalid type for format 'B'
>>> y = x.cast('c')
>>> y[0] = b'a'
>>> b
bytearray(b'ayz')

    Cast 1D/bytes to 3D/ints to 1D/signed char: 

    >>> import struct
>>> buf = struct.pack("i"*12, *list(range(12)))
>>> x = memoryview(buf)
>>> y = x.cast('i', shape=[2,2,3])
>>> y.tolist()
[[[0, 1, 2], [3, 4, 5]], [[6, 7, 8], [9, 10, 11]]]
>>> y.format
'i'
>>> y.itemsize
4
>>> len(y)
2
>>> y.nbytes
48
>>> z = y.cast('b')
>>> z.format
'b'
>>> z.itemsize
1
>>> len(z)
48
>>> z.nbytes
48

    Cast 1D/unsigned long to 2D/unsigned long: 

    >>> buf = struct.pack("L"*6, *list(range(6)))
>>> x = memoryview(buf)
>>> y = x.cast('L', shape=[2,3])
>>> len(y)
2
>>> y.nbytes
48
>>> y.tolist()
[[0, 1, 2], [3, 4, 5]]

    Added in version 3.3.

    3.5 版改变： 不再限定源格式当铸造成字节视图时。

    还有几个可用只读属性：

    obj ¶

    底层 memoryview 对象： 

    >>> b  = bytearray(b'xyz')
>>> m = memoryview(b)
>>> m.obj is b
True

    Added in version 3.3.

    nbytes ¶

    nbytes == product(shape) * itemsize == len(m.tobytes()) . This is the amount of space in bytes that the array would use in a contiguous representation. It is not necessarily equal to len(m) : 

    >>> import array
>>> a = array.array('i', [1,2,3,4,5])
>>> m = memoryview(a)
>>> len(m)
5
>>> m.nbytes
20
>>> y = m[::2]
>>> len(y)
3
>>> y.nbytes
12
>>> len(y.tobytes())
12

    多维数组： 

    >>> import struct
>>> buf = struct.pack("d"*12, *[1.5*x for x in range(12)])
>>> x = memoryview(buf)
>>> y = x.cast('d', shape=[3,4])
>>> y.tolist()
[[0.0, 1.5, 3.0, 4.5], [6.0, 7.5, 9.0, 10.5], [12.0, 13.5, 15.0, 16.5]]
>>> len(y)
3
>>> y.nbytes
96

    Added in version 3.3.

    readonly ¶

    A bool indicating whether the memory is read only.

    format ¶

    A string containing the format (in struct module style) for each element in the view. A memoryview can be created from exporters with arbitrary format strings, but some methods (e.g. tolist() ) are restricted to native single element formats.

    3.3 版改变： format 'B' is now handled according to the struct module syntax. This means that memoryview(b'abc')[0] == b'abc'[0] == 97 .

    itemsize ¶

    The size in bytes of each element of the memoryview: 

    >>> import array, struct
>>> m = memoryview(array.array('H', [32000, 32001, 32002]))
>>> m.itemsize
2
>>> m[0]
32000
>>> struct.calcsize('H') == m.itemsize
True
    ndim ¶

    An integer indicating how many dimensions of a multi-dimensional array the memory represents.

    shape ¶

    A tuple of integers the length of ndim giving the shape of the memory as an N-dimensional array.

    3.3 版改变： An empty tuple instead of None when ndim = 0.

    strides ¶

    A tuple of integers the length of ndim giving the size in bytes to access each element for each dimension of the array.

    3.3 版改变： An empty tuple instead of None when ndim = 0.

    suboffsets ¶

    Used internally for PIL-style arrays. The value is informational only.

    c_contiguous ¶

    A bool indicating whether the memory is C- contiguous .

    Added in version 3.3.

    f_contiguous ¶

    A bool indicating whether the memory is Fortran contiguous .

    Added in version 3.3.

    contiguous ¶

    A bool indicating whether the memory is contiguous .

    Added in version 3.3.

    集类型 — set , frozenset ¶

    A set 对象是无序集合的截然不同 hashable objects. Common uses include membership testing, removing duplicates from a sequence, and computing mathematical operations such as intersection, union, difference, and symmetric difference. (For other containers see the built-in dict , list ，和 tuple 类，和 collections 模块。)

    Like other collections, sets support x in set , len(set) ，和 for x in set . Being an unordered collection, sets do not record element position or order of insertion. Accordingly, sets do not support indexing, slicing, or other sequence-like behavior.

    There are currently two built-in set types, set and frozenset 。 set type is mutable — the contents can be changed using methods like add() and remove() . Since it is mutable, it has no hash value and cannot be used as either a dictionary key or as an element of another set. The frozenset type is immutable and hashable — its contents cannot be altered after it is created; it can therefore be used as a dictionary key or as an element of another set.

    Non-empty sets (not frozensets) can be created by placing a comma-separated list of elements within braces, for example: {'jack', 'sjoerd'} , in addition to the set 构造函数。

    这 2 个类的构造函数工作方式相同：

    class set ( [ iterable ] ) ¶
    class frozenset ( [ iterable ] ) ¶

    返回新 set 或 frozenset 对象的元素取自 iterable 。集元素必须 hashable 。要表示集的集，内部集必须是 frozenset 对象。若 iterable 未指定，返回新的空集。

    可以按几种方式创建集：

    • 使用在花括号内的逗号分隔元素列表： {'jack', 'sjoerd'}

    • 使用集推导： {c for c in 'abracadabra' if c not in 'abc'}

    • 使用类型构造函数： set() , set('foobar') , set(['a', 'b', 'foo'])

    实例化的 set and frozenset 提供以下操作：

    len(s)

    返回元素的数量对于集 s (基数对于 s ).

    x in s

    测试 x 为成员资格在 s .

    x not in s

    测试 x 为非成员资格在 s .

    isdisjoint ( other ) ¶

    返回 True 若集没有元素相同于 other 。集不相交当且仅当它们的交集为空集时。

    issubset ( other ) ¶
    set <= other

    测试集中的每一元素是否都在 other .

    set < other

    Test whether the set is a proper subset of other ，也就是说， set <= other and set != other .

    issuperset ( other ) ¶
    set >= other

    Test whether every element in other is in the set.

    set > other

    Test whether the set is a proper superset of other ，也就是说， set >= other and set != other .

    union ( * others ) ¶
    set | other | ...

    返回带有集和所有其它 others 的元素的新集。

    intersection ( * others ) ¶
    set & other & ...

    返回带有集和所有 others 的共有元素的新集。

    difference ( * others ) ¶
    set - other - ...

    返回新集，且集元素中不在 others 中。

    symmetric_difference ( other ) ¶
    set ^ other

    Return a new set with elements in either the set or other but not both.

    copy ( ) ¶

    返回集的浅拷贝。

    注意，非运算符版本的 union() , intersection() , difference() , symmetric_difference() , issubset() ，和 issuperset() methods will accept any iterable as an argument. In contrast, their operator based counterparts require their arguments to be sets. This precludes error-prone constructions like set('abc') & 'cbs' in favor of the more readable set('abc').intersection('cbs') .

    Both set and frozenset support set to set comparisons. Two sets are equal if and only if every element of each set is contained in the other (each is a subset of the other). A set is less than another set if and only if the first set is a proper subset of the second set (is a subset, but is not equal). A set is greater than another set if and only if the first set is a proper superset of the second set (is a superset, but is not equal).

    实例化的 set are compared to instances of frozenset based on their members. For example, set('abc') == frozenset('abc') 返回 True and so does set('abc') in set([frozenset('abc')]) .

    The subset and equality comparisons do not generalize to a total ordering function. For example, any two nonempty disjoint sets are not equal and are not subsets of each other, so all of the following return False : a<b , a==b ，或 a>b .

    Since sets only define partial ordering (subset relationships), the output of the list.sort() method is undefined for lists of sets.

    像字典键的集元素必须 hashable .

    二进制操作混合 set 实例与 frozenset return the type of the first operand. For example: frozenset('ab') | set('bc') 返回实例化的 frozenset .

    The following table lists operations available for set that do not apply to immutable instances of frozenset :

    update ( * others ) ¶
    set |= other | ...

    更新集，添加来自所有 others 的元素。

    intersection_update ( * others ) ¶
    set &= other & ...

    更新集，仅保持在它和所有 others 中找到的元素。

    difference_update ( * others ) ¶
    set -= other | ...

    更新集，移除在 others 中找到的元素。

    symmetric_difference_update ( other ) ¶
    set ^= other

    更新集，只保持在集中找到的元素，而不是两者中的元素。

    add ( elem ) ¶

    添加元素 elem 到集。

    remove ( elem ) ¶

    移除元素 elem 从集。引发 KeyError if elem 未包含在集中。

    discard ( elem ) ¶

    移除元素 elem 从集，若存在。

    pop ( ) ¶

    移除并返回任意集元素。引发 KeyError 若集为空。

    clear ( ) ¶

    移除所有集元素。

    注意，非运算符版本的 update() , intersection_update() , difference_update() ，和 symmetric_difference_update() 方法将接受任何可迭代作为自变量。

    注意： elem 自变量到 __contains__() , remove() ，和 discard() 方法可能有设置。为支持搜索等效冻结集，临时创建一个从 elem .

    映射类型 — dict ¶

    A 映射 对象映射 hashable 值到任意对象。映射是可变对象。目前只有一种标准映射类型， dictionary 。(对于其它容器，见内置 list , set ，和 tuple 类，和 collections 模块。)

    字典键是 almost 任意值。值不 hashable , that is, values containing lists, dictionaries or other mutable types (that are compared by value rather than by object identity) may not be used as keys. Values that compare equal (such as 1 , 1.0 ，和 True ) can be used interchangeably to index the same dictionary entry.

    class dict ( ** kwargs ) ¶
    class dict ( 映射 , ** kwargs )
    class dict ( iterable , ** kwargs )

    返回初始化自可选位置自变量和一组可能为空的关键词自变量的新字典。

    可以按几种方式创建字典：

    • 使用逗号分隔的列表 key: value 对在花括号内： {'jack': 4098, 'sjoerd': 4127} or {4098: 'jack', 4127: 'sjoerd'}

    • 使用字典推导： {} , {x: x ** 2 for x in range(10)}

    • 使用类型构造函数： dict() , dict([('foo', 100), ('bar', 200)]) , dict(foo=100, bar=200)

    若位置自变量未给定，创建空字典。若位置自变量有给定且是映射对象，创建字典具有如映射对象的相同键值对。否则，位置自变量必须是 iterable 对象。iterable (可迭代) 中的各项本身必须是恰好具有 2 对象的可迭代。各项的第 1 对象变为新字典键，而第 2 对象变为相应值。若键有出现多次，该键的最后值变为新字典相应值。

    若关键词自变量有给定，关键词自变量及其值会被添加到从位置自变量创建的字典。若要添加的 key (键) 已存在，来自关键词自变量的 value (值) 会替换来自位置自变量的值。

    为阐明，下列范例返回的字典都等于 {"one": 1, "two": 2, "three": 3} : 

    >>> a = dict(one=1, two=2, three=3)
>>> b = {'one': 1, 'two': 2, 'three': 3}
>>> c = dict(zip(['one', 'two', 'three'], [1, 2, 3]))
>>> d = dict([('two', 2), ('one', 1), ('three', 3)])
>>> e = dict({'three': 3, 'one': 1, 'two': 2})
>>> f = dict({'one': 1, 'three': 3}, two=2)
>>> a == b == c == d == e == f
True

    如第 1 范例提供的关键词自变量，仅工作于有效 Python 标识符键。否则，可以使用任何有效 key (键)。

    这些是字典支持的操作 (因此，自定义映射类型也应该支持)：

    list(d)

    返回所有键的列表对于字典 d .

    len(d)

    返回项数对于字典 d .

    d[key]

    返回项在 d 采用键 key 。引发 KeyError if key 不在映射中。

    若字典的子类有定义方法 __missing__() and key 不存在， d[key] 操作将调用该方法采用键 key 作为自变量。 d[key] 操作然后返回或引发返回任何或被引发通过 __missing__(key) 调用。其它操作或方法不会援引 __missing__() 。若 __missing__() 未定义， KeyError 被引发。 __missing__() 必须是方法；它不能是实例变量： 

    >>> class Counter(dict):
...     def __missing__(self, key):
...         return 0
...
>>> c = Counter()
>>> c['red']
0
>>> c['red'] += 1
>>> c['red']
1

    以上范例展示部分实现为 collections.Counter 。不同 __missing__ 方法被用于 collections.defaultdict .

    d[key] = value

    Set d[key] to value .

    del d[key]

    移除 d[key] from d 。引发 KeyError if key 不在映射中。

    key in d

    返回 True if d 拥有键 key ，否则 False .

    key not in d

    相当于 not key in d .

    iter(d)

    返回覆盖字典键的迭代器。这是快捷方式为 iter(d.keys()) .

    clear ( ) ¶

    移除所有项从字典。

    copy ( ) ¶

    返回字典的浅拷贝。

    classmethod fromkeys ( iterable , value = None ) ¶

    创建新字典采用键来自 iterable 并把值设为 value .

    fromkeys() 是返回新字典的类方法。 value 默认为 None 。所有值仅引用单一实例，因此通常没有意义若 value 是可变对象 (譬如：空列表)。要获得截然不同值，使用 字典推导 代替。

    get ( key , default = None ) ¶

    返回值为 key if key 在字典中，否则 default 。若 default 不给定，默认为 None ，因此此方法从不引发 KeyError .

    items ( ) ¶

    返回新视图为字典项 ( (key, value) 对)。见 视图对象的文档编制 .

    keys ( ) ¶

    返回字典键的新视图。见 视图对象的文档编制 .

    pop ( key [ , default ] ) ¶

    若 key 在字典中，移除它并返回其值，否则返回 default 。若 default 未给定且 key 不在字典中， KeyError 被引发。

    popitem ( ) ¶

    移除并返回 (key, value) 对从字典。对的返回按 LIFO 次序。

    popitem() 对破坏性迭代字典很有用，这常用于集合算法。若字典为空，调用 popitem() 引发 KeyError .

    3.7 版改变： LIFO (后进先出) 次序现在是保证的。在之前版本中， popitem() 将返回任意键/值对。

    reversed(d)

    返回字典键的反向迭代器。这是快捷方式对于 reversed(d.keys()) .

    Added in version 3.8.

    setdefault ( key , default = None ) ¶

    若 key 在字典中，返回其值。若不在，插入 key 采用值 default 并返回 default . default 默认为 None .

    update ( [ other ] ) ¶

    更新字典采用键/值对来自 other ，覆写现有键。返回 None .

    update() 接受另一字典对象或键/值对可迭代 (作为 2 长元组或其它可迭代)。若指定关键词自变量，则采用这些键/值对更新字典： d.update(red=1, blue=2) .

    values ( ) ¶

    返回字典值的新视图。见 视图对象的文档编制 .

    相等比较介于一 dict.values() 视图和另一将始终返回 False 。这也适用当比较 dict.values() 对自身： 

    >>> d = {'a': 1}
>>> d.values() == d.values()
False
    d | other

    Create a new dictionary with the merged keys and values of d and other , which must both be dictionaries. The values of other take priority when d and other share keys.

    Added in version 3.9.

    d |= other

    Update the dictionary d with keys and values from other , which may be either a 映射 或 iterable of key/value pairs. The values of other take priority when d and other share keys.

    Added in version 3.9.

    字典比较相等，当且仅当它们拥有相同 (key, value) 对 (不管次序)。次序比较 (<、<=、>=、>) 引发 TypeError .

    字典保留插入次序。注意，更新键不影响次序。删除后添加的键插入在末尾。 

    >>> d = {"one": 1, "two": 2, "three": 3, "four": 4}
>>> d
{'one': 1, 'two': 2, 'three': 3, 'four': 4}
>>> list(d)
['one', 'two', 'three', 'four']
>>> list(d.values())
[1, 2, 3, 4]
>>> d["one"] = 42
>>> d
{'one': 42, 'two': 2, 'three': 3, 'four': 4}
>>> del d["two"]
>>> d["two"] = None
>>> d
{'one': 42, 'three': 3, 'four': 4, 'two': None}

    3.7 版改变： 字典次序对插入次序是有保证的。此行为是从 CPython 3.6 起的实现细节。

    字典和字典视图是可逆的。 

    >>> d = {"one": 1, "two": 2, "three": 3, "four": 4}
>>> d
{'one': 1, 'two': 2, 'three': 3, 'four': 4}
>>> list(reversed(d))
['four', 'three', 'two', 'one']
>>> list(reversed(d.values()))
[4, 3, 2, 1]
>>> list(reversed(d.items()))
[('four', 4), ('three', 3), ('two', 2), ('one', 1)]

    3.8 版改变： 字典现在是可逆的。

    另请参阅

    types.MappingProxyType 可以用于创建只读视图的 dict .

    字典视图对象 ¶

    对象返回通过 dict.keys() , dict.values() and dict.items() are 视图对象 . They provide a dynamic view on the dictionary’s entries, which means that when the dictionary changes, the view reflects these changes.

    Dictionary views can be iterated over to yield their respective data, and support membership tests:

    len(dictview)

    返回字典条目数。

    iter(dictview)

    Return an iterator over the keys, values or items (represented as tuples of (key, value) ) 在字典中。

    Keys and values are iterated over in insertion order. This allows the creation of (value, key) pairs using zip() : pairs = zip(d.values(), d.keys()) . Another way to create the same list is pairs = [(v, k) for (k, v) in d.items()] .

    Iterating views while adding or deleting entries in the dictionary may raise a RuntimeError or fail to iterate over all entries.

    3.7 版改变： Dictionary order is guaranteed to be insertion order.

    x in dictview

    返回 True if x is in the underlying dictionary’s keys, values or items (in the latter case, x 应该为 (key, value) 元组)。

    reversed(dictview)

    Return a reverse iterator over the keys, values or items of the dictionary. The view will be iterated in reverse order of the insertion.

    3.8 版改变： 字典视图现在是可逆的。

    dictview.mapping

    返回 types.MappingProxyType that wraps the original dictionary to which the view refers.

    Added in version 3.10.

    Keys views are set-like since their entries are unique and hashable . Items views also have set-like operations since the (key, value) pairs are unique and the keys are hashable. If all values in an items view are hashable as well, then the items view can interoperate with other sets. (Values views are not treated as set-like since the entries are generally not unique.) For set-like views, all of the operations defined for the abstract base class collections.abc.Set are available (for example, == , < ，或 ^ ). While using set operators, set-like views accept any iterable as the other operand, unlike sets which only accept sets as the input.

    字典视图的用法范例： 

    >>> dishes = {'eggs': 2, 'sausage': 1, 'bacon': 1, 'spam': 500}
>>> keys = dishes.keys()
>>> values = dishes.values()
>>> # iteration
>>> n = 0
>>> for val in values:
...     n += val
...
>>> print(n)
504
>>> # keys and values are iterated over in the same order (insertion order)
>>> list(keys)
['eggs', 'sausage', 'bacon', 'spam']
>>> list(values)
[2, 1, 1, 500]
>>> # view objects are dynamic and reflect dict changes
>>> del dishes['eggs']
>>> del dishes['sausage']
>>> list(keys)
['bacon', 'spam']
>>> # set operations
>>> keys & {'eggs', 'bacon', 'salad'}
{'bacon'}
>>> keys ^ {'sausage', 'juice'} == {'juice', 'sausage', 'bacon', 'spam'}
True
>>> keys | ['juice', 'juice', 'juice'] == {'bacon', 'spam', 'juice'}
True
>>> # get back a read-only proxy for the original dictionary
>>> values.mapping
mappingproxy({'bacon': 1, 'spam': 500})
>>> values.mapping['spam']
500

    上下文管理器类型 ¶

    Python 的 with 语句支持由上下文管理器定义的运行时上下文概念。这是使用允许用户定义的类来定义在执行语句本体前进入运行时上下文，并在语句结束时退出的一对方法实现的：

    contextmanager. __enter__ ( ) ¶

    Enter the runtime context and return either this object or another object related to the runtime context. The value returned by this method is bound to the identifier in the as clause of with statements using this context manager.

    An example of a context manager that returns itself is a 文件对象 . File objects return themselves from __enter__() to allow open() to be used as the context expression in a with 语句。

    An example of a context manager that returns a related object is the one returned by decimal.localcontext() . These managers set the active decimal context to a copy of the original decimal context and then return the copy. This allows changes to be made to the current decimal context in the body of the with statement without affecting code outside the with 语句。

    contextmanager. __exit__ ( exc_type , exc_val , exc_tb ) ¶

    Exit the runtime context and return a Boolean flag indicating if any exception that occurred should be suppressed. If an exception occurred while executing the body of the with statement, the arguments contain the exception type, value and traceback information. Otherwise, all three arguments are None .

    Returning a true value from this method will cause the with statement to suppress the exception and continue execution with the statement immediately following the with statement. Otherwise the exception continues propagating after this method has finished executing. Exceptions that occur during execution of this method will replace any exception that occurred in the body of the with 语句。

    The exception passed in should never be reraised explicitly - instead, this method should return a false value to indicate that the method completed successfully and does not want to suppress the raised exception. This allows context management code to easily detect whether or not an __exit__() method has actually failed.

    Python defines several context managers to support easy thread synchronisation, prompt closure of files or other objects, and simpler manipulation of the active decimal arithmetic context. The specific types are not treated specially beyond their implementation of the context management protocol. See the contextlib module for some examples.

    Python 的 generator s and the contextlib.contextmanager decorator provide a convenient way to implement these protocols. If a generator function is decorated with the contextlib.contextmanager decorator, it will return a context manager implementing the necessary __enter__() and __exit__() methods, rather than the iterator produced by an undecorated generator function.

    Note that there is no specific slot for any of these methods in the type structure for Python objects in the Python/C API. Extension types wanting to define these methods must provide them as a normal Python accessible method. Compared to the overhead of setting up the runtime context, the overhead of a single class dictionary lookup is negligible.

    类型注解类型 — 一般别名 , Union ¶

    核心内置类型对于 类型注解 are 一般别名 and Union .

    一般别名类型 ¶

    GenericAlias 对象的创建一般来说是通过 subscripting 类。它们最常用于 容器类 ，譬如 list or dict 。例如， list[int] 是 GenericAlias 对象创建通过下标 list 类采用自变量 int . GenericAlias 对象首要旨在用于 类型注解 .

    注意

    It is generally only possible to subscript a class if the class implements the special method __class_getitem__() .

    A GenericAlias object acts as a proxy for a 一般类型 ，实现 参数化泛型 .

    For a container class, the argument(s) supplied to a subscription of the class may indicate the type(s) of the elements an object contains. For example, set[bytes] can be used in type annotations to signify a set in which all the elements are of type bytes .

    For a class which defines __class_getitem__() but is not a container, the argument(s) supplied to a subscription of the class will often indicate the return type(s) of one or more methods defined on an object. For example, regular expressions can be used on both the str data type and the bytes data type:

    • 若 x = re.search('foo', 'foo') , x 将是 re.Match object where the return values of x.group(0) and x[0] will both be of type str . We can represent this kind of object in type annotations with the GenericAlias re.Match[str] .

    • 若 y = re.search(b'bar', b'bar') ，(注意 b for bytes ), y will also be an instance of re.Match , but the return values of y.group(0) and y[0] will both be of type bytes . In type annotations, we would represent this variety of re.Match objects with re.Match[bytes] .

    GenericAlias 对象是实例化的类 types.GenericAlias ，也可以用于创建 GenericAlias 对象直接。

    T[X, Y, ...]

    创建 GenericAlias 表示类型 T parameterized by types X , Y , and more depending on the T used. For example, a function expecting a list 包含 float 元素： 

    def average(values: list[float]) -> float:
    return sum(values) / len(values)

    Another example for 映射 对象，使用 dict , which is a generic type expecting two type parameters representing the key type and the value type. In this example, the function expects a dict with keys of type str and values of type int : 

    def send_post_request(url: str, body: dict[str, int]) -> None:
    ...

    内置函数 isinstance() and issubclass() 不接受 GenericAlias 类型对于其第 2 自变量： 

    >>> isinstance([1, 2], list[str])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: isinstance() argument 2 cannot be a parameterized generic

    The Python runtime does not enforce 类型注解 . This extends to generic types and their type parameters. When creating a container object from a GenericAlias , the elements in the container are not checked against their type. For example, the following code is discouraged, but will run without errors: 

    >>> t = list[str]
>>> t([1, 2, 3])
[1, 2, 3]

    Furthermore, parameterized generics erase type parameters during object creation: 

    >>> t = list[str]
>>> type(t)
<class 'types.GenericAlias'>
>>> l = t()
>>> type(l)
<class 'list'>

    调用 repr() or str() 对于参数化类型的一般展示： 

    >>> repr(list[int])
'list[int]'
>>> str(list[int])
'list[int]'

    The __getitem__() method of generic containers will raise an exception to disallow mistakes like dict[str][str] : 

    >>> dict[str][str]
Traceback (most recent call last):
  ...
TypeError: dict[str] is not a generic class

    不管怎样，这种表达式是有效的当 类型变量 are used. The index must have as many elements as there are type variable items in the GenericAlias 对象的 __args__ . 

    >>> from typing import TypeVar
>>> Y = TypeVar('Y')
>>> dict[str, Y][int]
dict[str, int]

    标准泛型类 ¶

    以下标准库类支持参数化泛型。此列表不详尽。

    • tuple

    • list

    • dict

    • set

    • frozenset

    • type

    • collections.deque

    • collections.defaultdict

    • collections.OrderedDict

    • collections.Counter

    • collections.ChainMap

    • collections.abc.Awaitable

    • collections.abc.Coroutine

    • collections.abc.AsyncIterable

    • collections.abc.AsyncIterator

    • collections.abc.AsyncGenerator

    • collections.abc.Iterable

    • collections.abc.Iterator

    • collections.abc.Generator

    • collections.abc.Reversible

    • collections.abc.Container

    • collections.abc.Collection

    • collections.abc.Callable

    • collections.abc.Set

    • collections.abc.MutableSet

    • collections.abc.Mapping

    • collections.abc.MutableMapping

    • collections.abc.Sequence

    • collections.abc.MutableSequence

    • collections.abc.ByteString

    • collections.abc.MappingView

    • collections.abc.KeysView

    • collections.abc.ItemsView

    • collections.abc.ValuesView

    • contextlib.AbstractContextManager

    • contextlib.AbstractAsyncContextManager

    • dataclasses.Field

    • functools.cached_property

    • functools.partialmethod

    • os.PathLike

    • queue.LifoQueue

    • queue.Queue

    • queue.PriorityQueue

    • queue.SimpleQueue

    • re.Pattern

    • re.Match

    • shelve.BsdDbShelf

    • shelve.DbfilenameShelf

    • shelve.Shelf

    • types.MappingProxyType

    • weakref.WeakKeyDictionary

    • weakref.WeakMethod

    • weakref.WeakSet

    • weakref.WeakValueDictionary

    特殊属性对于 GenericAlias 对象 ¶

    所有参数化泛型，实现特殊只读属性。

    genericalias. __origin__ ¶

    This attribute points at the non-parameterized generic class: 

    >>> list[int].__origin__
<class 'list'>
    genericalias. __args__ ¶

    此属性是 tuple (possibly of length 1) of generic types passed to the original __class_getitem__() of the generic class: 

    >>> dict[str, list[int]].__args__
(<class 'str'>, list[int])
    genericalias. __parameters__ ¶

    This attribute is a lazily computed tuple (possibly empty) of unique type variables found in __args__ : 

    >>> from typing import TypeVar
>>> T = TypeVar('T')
>>> list[T].__parameters__
(~T,)

    注意

    A GenericAlias 对象采用 typing.ParamSpec parameters may not have correct __parameters__ after substitution because typing.ParamSpec is intended primarily for static type checking.

    genericalias. __unpacked__ ¶

    A boolean that is true if the alias has been unpacked using the * 运算符 (见 TypeVarTuple ).

    Added in version 3.11.

    另请参阅

    PEP 484 - 类型提示

    Introducing Python’s framework for type annotations.

    PEP 585 - Type Hinting Generics In Standard Collections

    Introducing the ability to natively parameterize standard-library classes, provided they implement the special class method __class_getitem__() .

    一般 , 用户定义泛型 and typing.Generic

    Documentation on how to implement generic classes that can be parameterized at runtime and understood by static type-checkers.

    Added in version 3.9.

    Union 类型 ¶

    Union (并集) 对象保持值为 | (按位 OR) 操作对于多个 类型对象 。这些类型首要旨在用于 类型注解 . The union type expression enables cleaner type hinting syntax compared to typing.Union .

    X | Y | ...

    Defines a union object which holds types X , Y , and so forth. X | Y means either X or Y. It is equivalent to typing.Union[X, Y] . For example, the following function expects an argument of type int or float : 

    def square(number: int | float) -> int | float:
    return number ** 2

    注意

    The | operand cannot be used at runtime to define unions where one or more members is a forward reference. For example, int | "Foo" ，其中 "Foo" is a reference to a class not yet defined, will fail at runtime. For unions which include forward references, present the whole expression as a string, e.g. "int | Foo" .

    union_object == other

    Union objects can be tested for equality with other union objects. Details:

    • Unions of unions are flattened: 

      (int | str) | float == int | str | float

    • Redundant types are removed: 

      int | str | int == int | str

    • When comparing unions, the order is ignored: 

      int | str == str | int

    • It is compatible with typing.Union : 

      int | str == typing.Union[int, str]

    • Optional types can be spelled as a union with None : 

      str | None == typing.Optional[str]
    isinstance(obj, union_object)
    issubclass(obj, union_object)

    调用 isinstance() and issubclass() 还支持 Union 对象： 

    >>> isinstance("", int | str)
True

    不管怎样， 参数化泛型 in union objects cannot be checked: 

    >>> isinstance(1, int | list[int])  # short-circuit evaluation
True
>>> isinstance([1], int | list[int])
Traceback (most recent call last):
  ...
TypeError: isinstance() argument 2 cannot be a parameterized generic

    The user-exposed type for the union object can be accessed from types.UnionType and used for isinstance() checks. An object cannot be instantiated from the type: 

    >>> import types
>>> isinstance(int | str, types.UnionType)
True
>>> types.UnionType()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: cannot create 'types.UnionType' instances

    注意

    The __or__() method for type objects was added to support the syntax X | Y . If a metaclass implements __or__() , the Union may override it: 

    >>> class M(type):
...     def __or__(self, other):
...         return "Hello"
...
>>> class C(metaclass=M):
...     pass
...
>>> C | int
'Hello'
>>> int | C
int | C

    另请参阅

    PEP 604 – PEP proposing the X | Y syntax and the Union type.

    Added in version 3.10.

    其它内置类型 ¶

    解释器支持几种其它种类的对象。这些中的大多数只支持 1 种或 2 种操作。

    模块 ¶

    模块的唯一特殊操作是属性访问： m.name ，其中 m 是模块和 name 访问定义名称在 m 的符号表。可以赋值模块属性 (注意， import 语句严格来说，并未运转于模块对象； import foo 不要求命名模块对象 foo 的存在，相反，它要求 (外部) definition 对于命名模块 foo 在其它地方)。

    每个模块的特殊属性是 __dict__ 。这是包含模块符号表的字典。修改此字典实际上会改变模块的符号表，但直接赋值 __dict__ 属性是不可能的 (可以编写 m.__dict__['a'] = 1 ，其定义 m.a 到 1 ，但无法编写 m.__dict__ = {} )。修改 __dict__ 直接不推荐。

    将模块内置进解释器的编写像这样： <module 'sys' (built-in)> 。若从文件加载，它们被写成 <module 'os' from '/usr/local/lib/pythonX.Y/os.pyc'> .

    类和类实例 ¶

    见 对象、值及类型 and 类定义 对于这些。

    函数 ¶

    Function objects are created by function definitions. The only operation on a function object is to call it: func(argument-list) .

    There are really two flavors of function objects: built-in functions and user-defined functions. Both support the same operation (to call the function), but the implementation is different, hence the different object types.

    见 函数定义 了解更多信息。

    方法 ¶

    Methods are functions that are called using the attribute notation. There are two flavors: built-in methods (譬如 append() on lists) and class instance method . Built-in methods are described with the types that support them.

    If you access a method (a function defined in a class namespace) through an instance, you get a special object: a bound method (also called instance method ) object. When called, it will add the self argument to the argument list. Bound methods have two special read-only attributes: m.__self__ is the object on which the method operates, and m.__func__ is the function implementing the method. Calling m(arg-1, arg-2, ..., arg-n) is completely equivalent to calling m.__func__(m.__self__, arg-1, arg-2, ..., arg-n) .

    像 function objects , bound method objects support getting arbitrary attributes. However, since method attributes are actually stored on the underlying function object ( method.__func__ ), setting method attributes on bound methods is disallowed. Attempting to set an attribute on a method results in an AttributeError being raised. In order to set a method attribute, you need to explicitly set it on the underlying function object: 

    >>> class C:
...     def method(self):
...         pass
...
>>> c = C()
>>> c.method.whoami = 'my name is method'  # can't set on the method
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'method' object has no attribute 'whoami'
>>> c.method.__func__.whoami = 'my name is method'
>>> c.method.whoami
'my name is method'

    见 实例方法 了解更多信息。

    代码对象 ¶

    代码对象用于实现以表示 "伪编译" 可执行 Python 代码，譬如：函数本体。它们异于函数对象，因为它们不包含对其全局执行环境的引用。代码对象的返回是通过内置 compile() 函数且可以提取自函数对象透过它们的 __code__ 属性。另请参阅 code 模块。

    访问 __code__ 引发 审计事件 object.__getattr__ 采用自变量 obj and "__code__" .

    代码对象可以被执行或评估通过将它 (而不是源字符串) 传递给 exec() or eval() 内置函数。

    见 标准类型层次结构 了解更多信息。

    类型对象 ¶

    Type objects represent the various object types. An object’s type is accessed by the built-in function type() . There are no special operations on types. The standard module types defines names for all standard built-in types.

    类型写成像这样： <class 'int'> .

    Null 对象 ¶

    This object is returned by functions that don’t explicitly return a value. It supports no special operations. There is exactly one null object, named None (a built-in name). type(None)() produces the same singleton.

    它被写为 None .

    省略对象 ¶

    This object is commonly used by slicing (see 切片 ). It supports no special operations. There is exactly one ellipsis object, named Ellipsis (a built-in name). type(Ellipsis)() produces the Ellipsis singleton.

    它被写为 Ellipsis or ... .

    未实现对象 ¶

    This object is returned from comparisons and binary operations when they are asked to operate on types they don’t support. See 比较 for more information. There is exactly one NotImplemented 对象。 type(NotImplemented)() 产生单例实例。

    它被写为 NotImplemented .

    内部对象 ¶

    见 标准类型层次结构 for this information. It describes stack frame objects , traceback objects , and slice objects.

    特殊属性 ¶

    实现将一些相关特殊只读属性添加到对象类型。其中一些不报告通过 dir() 内置函数。

    对象。 __dict__ ¶

    用于存储对象 (可写) 属性的字典或其它映射对象。

    实例。 __class__ ¶

    类实例所属的类。

    类。 __bases__ ¶

    类对象的基类元组。

    定义。 __name__ ¶

    类、函数、方法、描述符或生成器实例的名称。

    定义。 __qualname__ ¶

    The 合格名称 对于类、函数、方法、描述符或生成器实例。

    Added in version 3.3.

    定义。 __type_params__ ¶

    The type parameters of generic classes, functions, and type aliases .

    3.12 版添加。

    类。 __mro__ ¶

    This attribute is a tuple of classes that are considered when looking for base classes during method resolution.

    类。 mro ( ) ¶

    This method can be overridden by a metaclass to customize the method resolution order for its instances. It is called at class instantiation, and its result is stored in __mro__ .

    类。 __subclasses__ ( ) ¶

    Each class keeps a list of weak references to its immediate subclasses. This method returns a list of all those references still alive. The list is in definition order. Example: 

    >>> int.__subclasses__()
[<class 'bool'>, <enum 'IntEnum'>, <flag 'IntFlag'>, <class 're._constants._NamedIntConstant'>]

    整数字符串转换长度局限性 ¶

    CPython 对转换有全局限制介于 int and str to mitigate denial of service attacks. This limit only applies to decimal or other non-power-of-two number bases. Hexadecimal, octal, and binary conversions are unlimited. The limit can be configured.

    The int type in CPython is an arbitrary length number stored in binary form (commonly known as a “bignum”). There exists no algorithm that can convert a string to a binary integer or a binary integer to a string in linear time, unless the base is a power of 2. Even the best known algorithms for base 10 have sub-quadratic complexity. Converting a large value such as int('1' * 500_000) can take over a second on a fast CPU.

    Limiting conversion size offers a practical way to avoid CVE-2020-10735 .

    The limit is applied to the number of digit characters in the input or output string when a non-linear conversion algorithm would be involved. Underscores and the sign are not counted towards the limit.

    When an operation would exceed the limit, a ValueError 被引发： 

    >>> import sys
>>> sys.set_int_max_str_digits(4300)  # Illustrative, this is the default.
>>> _ = int('2' * 5432)
Traceback (most recent call last):
...
ValueError: Exceeds the limit (4300 digits) for integer string conversion: value has 5432 digits; use sys.set_int_max_str_digits() to increase the limit
>>> i = int('2' * 4300)
>>> len(str(i))
4300
>>> i_squared = i*i
>>> len(str(i_squared))
Traceback (most recent call last):
...
ValueError: Exceeds the limit (4300 digits) for integer string conversion; use sys.set_int_max_str_digits() to increase the limit
>>> len(hex(i_squared))
7144
>>> assert int(hex(i_squared), base=16) == i*i  # Hexadecimal is unlimited.

    The default limit is 4300 digits as provided in sys.int_info.default_max_str_digits . The lowest limit that can be configured is 640 digits as provided in sys.int_info.str_digits_check_threshold .

    Verification: 

    >>> import sys
>>> assert sys.int_info.default_max_str_digits == 4300, sys.int_info
>>> assert sys.int_info.str_digits_check_threshold == 640, sys.int_info
>>> msg = int('578966293710682886880994035146873798396722250538762761564'
...           '9252925514383915483333812743580549779436104706260696366600'
...           '571186405732').to_bytes(53, 'big')
...

    Added in version 3.11.

    受影响 API ¶

    The limitation only applies to potentially slow conversions between int and str or bytes :

    • int(string) 采用默认基 10。

    • int(string, base) for all bases that are not a power of 2.

    • str(integer) .

    • repr(integer) .

    • any other string conversion to base 10, for example f"{integer}" , "{}".format(integer) ，或 b"%d" % integer .

    The limitations do not apply to functions with a linear algorithm:

    • int(string, base) 采用基 2、4、8、16 或 32。

    • int.from_bytes() and int.to_bytes() .

    • hex() , oct() , bin() .

    • 格式规范迷你语言 对于十六进制、八进制及二进制数。

    • str to float .

    • str to decimal.Decimal .

    配置限制 ¶

    Before Python starts up you can use an environment variable or an interpreter command line flag to configure the limit:

    • PYTHONINTMAXSTRDIGITS ，如 PYTHONINTMAXSTRDIGITS=640 python3 to set the limit to 640 or PYTHONINTMAXSTRDIGITS=0 python3 to disable the limitation.

    • -X int_max_str_digits ，如 python3 -X int_max_str_digits=640

    • sys.flags.int_max_str_digits 包含值 PYTHONINTMAXSTRDIGITS or -X int_max_str_digits . If both the env var and the -X option are set, the -X option takes precedence. A value of -1 indicates that both were unset, thus a value of sys.int_info.default_max_str_digits was used during initialization.

    From code, you can inspect the current limit and set a new one using these sys API：

    • sys.get_int_max_str_digits() and sys.set_int_max_str_digits() are a getter and setter for the interpreter-wide limit. Subinterpreters have their own limit.

    Information about the default and minimum can be found in sys.int_info :

    • sys.int_info.default_max_str_digits is the compiled-in default limit.

    • sys.int_info.str_digits_check_threshold is the lowest accepted value for the limit (other than 0 which disables it).

    Added in version 3.11.

    Caution

    Setting a low limit can lead to problems. While rare, code exists that contains integer constants in decimal in their source that exceed the minimum threshold. A consequence of setting the limit is that Python source code containing decimal integer literals longer than the limit will encounter an error during parsing, usually at startup time or import time or even at installation time - anytime an up to date .pyc does not already exist for the code. A workaround for source that contains such large constants is to convert them to 0x hexadecimal form as it has no limit.

    Test your application thoroughly if you use a low limit. Ensure your tests run with the limit set early via the environment or flag so that it applies during startup and even during any installation step that may invoke Python to precompile .py 源到 .pyc 文件。

    推荐配置 ¶

    默认 sys.int_info.default_max_str_digits is expected to be reasonable for most applications. If your application requires a different limit, set it from your main entry point using Python version agnostic code as these APIs were added in security patch releases in versions before 3.12.

    范例： 

    >>> import sys
>>> if hasattr(sys, "set_int_max_str_digits"):
...     upper_bound = 68000
...     lower_bound = 4004
...     current_limit = sys.get_int_max_str_digits()
...     if current_limit == 0 or current_limit > upper_bound:
...         sys.set_int_max_str_digits(upper_bound)
...     elif current_limit < lower_bound:
...         sys.set_int_max_str_digits(lower_bound)

    若需要完全禁用，将它设为 0 .

    脚注

    [ 1 ]

    Additional information on these special methods may be found in the Python Reference Manual ( 基本定制 ).

    [ 2 ]

    因此，列表 [1, 2] 被认为等于 [1.0, 2.0] ，且类似元组。

    [ 3 ]

    They must have since the parser can’t tell the type of the operands.

    [ 4 ] ( 1 , 2 , 3 , 4 )

    Cased characters are those with general category property being one of “Lu” (Letter, uppercase), “Ll” (Letter, lowercase), or “Lt” (Letter, titlecase).

    [ 5 ] ( 1 , 2 )

    To format only a tuple you should therefore provide a singleton tuple whose only element is the tuple to be formatted.

    内容表

    • 内置类型
      • 真值测试
      • 布尔运算 — and , or , not
      • 比较
      • 数值类型 — int , float , complex
        • 整数类型的按位运算
        • 额外整数类型方法
        • 额外浮点方法
        • 数值类型的哈希
      • Boolean Type - bool
      • 迭代器类型
        • 生成器类型
      • 序列类型 — list , tuple , range
        • 常见序列操作
        • 不可变序列类型
        • 可变序列类型
        • 列表
        • 元组
        • 范围
      • 文本序列类型 — str
        • 字符串方法
        • printf 样式字符串格式化
      • 二进制序列类型 — bytes , bytearray , memoryview
        • bytes 对象
        • bytearray 对象
        • bytes 和 bytearray 操作
        • printf 样式字节格式化
        • 内存视图
      • 集类型 — set , frozenset
      • 映射类型 — dict
        • 字典视图对象
      • 上下文管理器类型
      • 类型注解类型 — 一般别名 , Union
        • 一般别名类型
          • 标准泛型类
          • 特殊属性对于 GenericAlias 对象
        • Union 类型
      • 其它内置类型
        • 模块
        • 类和类实例
        • 函数
        • 方法
        • 代码对象
        • 类型对象
        • Null 对象
        • 省略对象
        • 未实现对象
        • 内部对象
      • 特殊属性
      • 整数字符串转换长度局限性
        • 受影响 API
        • 配置限制
        • 推荐配置

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