Python 解释器内置了许多始终可用的函数和类型。在此按字母顺序列表它们。
abs
(
x
)
¶
返回数的绝对值。自变量可以是整数或浮点数。若自变量是复数，则返回其振幅。
all
(
iterable
)
¶
返回
True
若所有元素在
iterable
为 true (或者若可迭代为空)。相当于：
def all(iterable):
for element in iterable:
if not element:
return False
return True
any
(
iterable
)
¶
返回
True
若任何元素在
iterable
为 true。若可迭代为空，返回
False
。相当于：
def any(iterable):
for element in iterable:
if element:
return True
return False
ascii
(
object
)
¶
As
repr()
, return a string containing a printable representation of an object, but escape the non-ASCII characters in the string returned by
repr()
使用
\x
,
\u
or
\U
escapes. This generates a string similar to that returned by
repr()
在 Python 2。
bin
(
x
)
¶
Convert an integer number to a binary string prefixed with “0b”. The result is a valid Python expression. If
x
is not a Python
int
object, it has to define an
__index__()
method that returns an integer. Some examples:
>>> bin(3)
'0b11'
>>> bin(-10)
'-0b1010'
If prefix “0b” is desired or not, you can use either of the following ways.
>>> format(14, '#b'), format(14, 'b')
('0b1110', '1110')
>>> f'{14:#b}', f'{14:b}'
('0b1110', '1110')
另请参阅
format()
了解更多信息。
bool
(
[
x
]
)
¶
返回布尔值，即：
True
or
False
.
x
的转换是使用标准
真值测试过程
。若
x
为 false 或被省略，这返回
False
；否则它返回
True
。
bool
类是子类化的
int
(见
数值类型 — int float complex
)。它无法进一步子类化。它的唯一实例是
False
and
True
(见
布尔值
).
bytearray
(
[
source
[
,
encoding
[
,
errors
]
]
]
)
返新字节数组。
bytearray
class is a mutable sequence of integers in the range 0 <= x < 256. It has most of the usual methods of mutable sequences, described in
可变序列类型
, as well as most methods that the
bytes
type has, see
bytes 和 bytearray 操作
.
可选 source parameter can be used to initialize the array in a few different ways:
bytearray()
then converts the string to bytes using
str.encode()
.
0
<=
x
<
256
, which are used as the initial contents of the array.
Without an argument, an array of size 0 is created.
另请参阅 二进制序列类型 — bytes、bytearray、memoryview and bytearray 对象 .
bytes
(
[
source
[
,
encoding
[
,
errors
]
]
]
)
返回新 bytes 对象，这是不可变整数序列，在范围
0
<=
x
<
256
.
bytes
是不可变版本的
bytearray
– 它拥有相同非变异方法、相同索引及切片行为。
故此，构造函数自变量的解释如同
bytearray()
.
也可以采用文字创建字节对象，见 字符串和 bytes 文字 .
另请参阅 二进制序列类型 — bytes、bytearray、memoryview , bytes 对象 ，和 bytes 和 bytearray 操作 .
callable
(
object
)
¶
返回
True
若
object
自变量看起来可调用，
False
if not. If this returns true, it is still possible that a call fails, but if it is false, calling
object
will never succeed. Note that classes are callable (calling a class returns a new instance); instances are callable if their class has a
__call__()
方法。
3.2 版新增： This function was first removed in Python 3.0 and then brought back in Python 3.2.
chr
(
i
)
¶
返回表示字符的字符串，其 Unicode 代码点是整数
i
。例如，
chr(97)
返回字符串
'a'
，而
chr(8364)
返回字符串
'€'
。这是逆对于
ord()
.
有效自变量范围是从 0 到 1,114,111 (以 16 为基的 0x10FFFF)。
ValueError
会被引发若
i
在该范围之外。
@
classmethod
¶
把方法变换成类方法。
A class method receives the class as implicit first argument, just like an instance method receives the instance. To declare a class method, use this idiom:
class C:
@classmethod
def f(cls, arg1, arg2, ...): ...
@classmethod
形式是函数
装饰器
– 见函数定义描述在
函数定义
了解细节。
It can be called either on the class (such as
C.f()
) or on an instance (such as
C().f()
). The instance is ignored except for its class. If a class method is called for a derived class, the derived class object is passed as the implied first argument.
Class methods are different than C++ or Java static methods. If you want those, see
staticmethod()
in this section.
For more information on class methods, consult the documentation on the standard type hierarchy in 标准类型层次结构 .
compile
(
source
,
filename
,
mode
,
flags=0
,
dont_inherit=False
,
optimize=-1
)
¶
编译
source
into a code or AST object. Code objects can be executed by
exec()
or
eval()
.
source
can either be a normal string, a byte string, or an AST object. Refer to the
ast
module documentation for information on how to work with AST objects.
filename
argument should give the file from which the code was read; pass some recognizable value if it wasn’t read from a file (
'<string>'
is commonly used).
mode
argument specifies what kind of code must be compiled; it can be
'exec'
if
source
consists of a sequence of statements,
'eval'
if it consists of a single expression, or
'single'
if it consists of a single interactive statement (in the latter case, expression statements that evaluate to something other than
None
will be printed).
可选自变量
flags
and
dont_inherit
control which
future statements
affect the compilation of
source
. If neither is present (or both are zero) the code is compiled with those future statements that are in effect in the code that is calling
compile()
。若
flags
argument is given and
dont_inherit
is not (or is zero) then the future statements specified by the
flags
argument are used in addition to those that would be used anyway. If
dont_inherit
is a non-zero integer then the
flags
argument is it – the future statements in effect around the call to compile are ignored.
Future statements are specified by bits which can be bitwise ORed together to specify multiple statements. The bitfield required to specify a given feature can be found as the
compiler_flag
attribute on the
_Feature
instance in the
__future__
模块。
自变量
optimize
specifies the optimization level of the compiler; the default value of
-1
selects the optimization level of the interpreter as given by
-O
options. Explicit levels are
0
(no optimization;
__debug__
is true),
1
(asserts are removed,
__debug__
is false) or
2
(docstrings are removed too).
此函数引发
SyntaxError
若编译源无效，和
ValueError
若 source 包含 null 字节。
若想要将 Python 代码剖析成 AST 表示，见
ast.parse()
.
注意
When compiling a string with multi-line code in
'single'
or
'eval'
mode, input must be terminated by at least one newline character. This is to facilitate detection of incomplete and complete statements in the
code
模块。
警告
It is possible to crash the Python interpreter with a sufficiently large/complex string when compiling to an AST object due to stack depth limitations in Python’s AST compiler.
3.2 版改变：
Allowed use of Windows and Mac newlines. Also input in
'exec'
mode does not have to end in a newline anymore. Added the
optimize
参数。
3.5 版改变：
先前，
TypeError
was raised when null bytes were encountered in
source
.
complex
(
[
real
[
,
imag
]
]
)
¶
Return a complex number with the value
real
+
imag
*1j or convert a string or number to a complex number. If the first parameter is a string, it will be interpreted as a complex number and the function must be called without a second parameter. The second parameter can never be a string. Each argument may be any numeric type (including complex). If
imag
is omitted, it defaults to zero and the constructor serves as a numeric conversion like
int
and
float
. If both arguments are omitted, returns
0j
.
注意
When converting from a string, the string must not contain whitespace around the central
+
or
-
运算符。例如，
complex('1+2j')
is fine, but
complex('1
+
2j')
引发
ValueError
.
复杂类型的描述在 数值类型 — int float complex .
3.6 版改变： 允许按代码文字下划线分组数字。
delattr
(
object
,
name
)
¶
这相对于
setattr()
。自变量是对象和字符串。字符串必须是对象属性名称之一。函数将删除命名属性，若提供对象允许。例如，
delattr(x,
'foobar')
相当于
del
x.foobar
.
dict
(
**kwarg
)
dict
(
映射
,
**kwarg
)
dict
(
iterable
,
**kwarg
)
创建新字典。
dict
对象是字典类。见
dict
and
映射类型 — dict
有关此类的文档编制。
对于其它容器，见内置
list
,
set
，和
tuple
类，及
collections
模块。
dir
(
[
object
]
)
¶
Without arguments, return the list of names in the current local scope. With an argument, attempt to return a list of valid attributes for that object.
If the object has a method named
__dir__()
, this method will be called and must return the list of attributes. This allows objects that implement a custom
__getattr__()
or
__getattribute__()
function to customize the way
dir()
reports their attributes.
若对象不提供
__dir__()
, the function tries its best to gather information from the object’s
__dict__
attribute, if defined, and from its type object. The resulting list is not necessarily complete, and may be inaccurate when the object has a custom
__getattr__()
.
默认
dir()
mechanism behaves differently with different types of objects, as it attempts to produce the most relevant, rather than complete, information:
结果列表按字母顺序排序。例如：
>>> import struct
>>> dir() # show the names in the module namespace
['__builtins__', '__name__', 'struct']
>>> dir(struct) # show the names in the struct module # doctest: +SKIP
['Struct', '__all__', '__builtins__', '__cached__', '__doc__', '__file__',
'__initializing__', '__loader__', '__name__', '__package__',
'_clearcache', 'calcsize', 'error', 'pack', 'pack_into',
'unpack', 'unpack_from']
>>> class Shape:
... def __dir__(self):
... return ['area', 'perimeter', 'location']
>>> s = Shape()
>>> dir(s)
['area', 'location', 'perimeter']
注意
因为
dir()
is supplied primarily as a convenience for use at an interactive prompt, it tries to supply an interesting set of names more than it tries to supply a rigorously or consistently defined set of names, and its detailed behavior may change across releases. For example, metaclass attributes are not in the result list when the argument is a class.
divmod
(
a
,
b
)
¶
Take two (non complex) numbers as arguments and return a pair of numbers consisting of their quotient and remainder when using integer division. With mixed operand types, the rules for binary arithmetic operators apply. For integers, the result is the same as
(a
//
b,
a
%
b)
. For floating point numbers the result is
(q,
a
%
b)
，其中
q
is usually
math.floor(a
/
b)
but may be 1 less than that. In any case
q
*
b
+
a
%
b
is very close to
a
, if
a
%
b
is non-zero it has the same sign as
b
，和
0
<=
abs(a
%
b)
<
abs(b)
.
enumerate
(
iterable
,
start=0
)
¶
返回枚举对象。
iterable
必须是序列，
iterator
，或支持迭代的某些其它对象。
__next__()
方法对于迭代器返回通过
enumerate()
返回元组包含计数 (从
start
其默认为 0) 和值获取自遍历
iterable
.
>>> seasons = ['Spring', 'Summer', 'Fall', 'Winter']
>>> list(enumerate(seasons))
[(0, 'Spring'), (1, 'Summer'), (2, 'Fall'), (3, 'Winter')]
>>> list(enumerate(seasons, start=1))
[(1, 'Spring'), (2, 'Summer'), (3, 'Fall'), (4, 'Winter')]
等效于：
def enumerate(sequence, start=0):
n = start
for elem in sequence:
yield n, elem
n += 1
eval
(
expression
,
globals=None
,
locals=None
)
¶
自变量是字符串和可选 globals 及 locals。若提供， globals 必须是字典。若提供， locals 可以是任何映射对象。
expression
argument is parsed and evaluated as a Python expression (technically speaking, a condition list) using the
globals
and
locals
dictionaries as global and local namespace. If the
globals
dictionary is present and does not contain a value for the key
__builtins__
, a reference to the dictionary of the built-in module
builtins
is inserted under that key before
expression
is parsed. This means that
expression
normally has full access to the standard
builtins
module and restricted environments are propagated. If the
locals
dictionary is omitted it defaults to the
globals
dictionary. If both dictionaries are omitted, the expression is executed in the environment where
eval()
is called. The return value is the result of the evaluated expression. Syntax errors are reported as exceptions. Example:
>>> x = 1
>>> eval('x+1')
2
This function can also be used to execute arbitrary code objects (such as those created by
compile()
). In this case pass a code object instead of a string. If the code object has been compiled with
'exec'
作为
mode
自变量，
eval()
的返回值将是
None
.
Hints: dynamic execution of statements is supported by the
exec()
function. The
globals()
and
locals()
functions returns the current global and local dictionary, respectively, which may be useful to pass around for use by
eval()
or
exec()
.
见
ast.literal_eval()
for a function that can safely evaluate strings with expressions containing only literals.
exec
(
object
[
,
globals
[
,
locals
]
]
)
¶
This function supports dynamic execution of Python code.
object
must be either a string or a code object. If it is a string, the string is parsed as a suite of Python statements which is then executed (unless a syntax error occurs).
[1]
If it is a code object, it is simply executed. In all cases, the code that’s executed is expected to be valid as file input (see the section “File input” in the Reference Manual). Be aware that the
return
and
yield
statements may not be used outside of function definitions even within the context of code passed to the
exec()
function. The return value is
None
.
In all cases, if the optional parts are omitted, the code is executed in the current scope. If only globals is provided, it must be a dictionary, which will be used for both the global and the local variables. If globals and locals are given, they are used for the global and local variables, respectively. If provided, locals can be any mapping object. Remember that at module level, globals and locals are the same dictionary. If exec gets two separate objects as globals and locals , the code will be executed as if it were embedded in a class definition.
若
globals
dictionary does not contain a value for the key
__builtins__
, a reference to the dictionary of the built-in module
builtins
is inserted under that key. That way you can control what builtins are available to the executed code by inserting your own
__builtins__
dictionary into
globals
before passing it to
exec()
.
filter
(
function
,
iterable
)
¶
Construct an iterator from those elements of
iterable
其中
function
returns true.
iterable
may be either a sequence, a container which supports iteration, or an iterator. If
function
is
None
, the identity function is assumed, that is, all elements of
iterable
that are false are removed.
注意，
filter(function,
iterable)
is equivalent to the generator expression
(item
for
item
in
iterable
if
function(item))
if function is not
None
and
(item
for
item
in
iterable
if
item)
if function is
None
.
见
itertools.filterfalse()
for the complementary function that returns elements of
iterable
其中
function
returns false.
float
(
[
x
]
)
¶
返回浮点数构造自数字或字符串 x .
If the argument is a string, it should contain a decimal number, optionally preceded by a sign, and optionally embedded in whitespace. The optional sign may be
'+'
or
'-'
; a
'+'
sign has no effect on the value produced. The argument may also be a string representing a NaN (not-a-number), or a positive or negative infinity. More precisely, the input must conform to the following grammar after leading and trailing whitespace characters are removed:
sign ::= "+" | "-" infinity ::= "Infinity" | "inf" nan ::= "nan" numeric_value ::=floatnumber|infinity|nannumeric_string ::= [sign]numeric_value
Here
floatnumber
is the form of a Python floating-point literal, described in
浮点文字
. Case is not significant, so, for example, “inf”, “Inf”, “INFINITY” and “iNfINity” are all acceptable spellings for positive infinity.
Otherwise, if the argument is an integer or a floating point number, a floating point number with the same value (within Python’s floating point precision) is returned. If the argument is outside the range of a Python float, an
OverflowError
会被引发。
对于一般 Python 对象
x
,
float(x)
委托
x.__float__()
.
若不给出自变量，
0.0
被返回。
范例：
>>> float('+1.23')
1.23
>>> float(' -12345\n')
-12345.0
>>> float('1e-003')
0.001
>>> float('+1E6')
1000000.0
>>> float('-Infinity')
-inf
浮点类型的描述在 数值类型 — int float complex .
3.6 版改变： 允许按代码文字下划线分组数字。
format
(
value
[
,
format_spec
]
)
¶
转换 value to a “formatted” representation, as controlled by format_spec . The interpretation of format_spec will depend on the type of the value argument, however there is a standard formatting syntax that is used by most built-in types: 格式规范的迷你语言 .
默认
format_spec
is an empty string which usually gives the same effect as calling
str(value)
.
调用
format(value,
format_spec)
is translated to
type(value).__format__(value,
format_spec)
which bypasses the instance dictionary when searching for the value’s
__format__()
method. A
TypeError
exception is raised if the method search reaches
object
和
format_spec
is non-empty, or if either the
format_spec
or the return value are not strings.
3.4 版改变：
object().__format__(format_spec)
引发
TypeError
if
format_spec
is not an empty string.
frozenset
(
[
iterable
]
)
返回新
frozenset
object, optionally with elements taken from
iterable
.
frozenset
is a built-in class. See
frozenset
and
Set Types — set, frozenset
有关此类的文档编制。
对于其它容器，见内置
set
,
list
,
tuple
，和
dict
类，及
collections
模块。
getattr
(
object
,
name
[
,
default
]
)
¶
返回命名属性的值为
object
.
name
必须是字符串。若字符串是对象属性名称之一，结果就是该属性的值。例如，
getattr(x,
'foobar')
相当于
x.foobar
。若命名属性不存在，
default
被返回若有提供，否则
AttributeError
被引发。
globals
(
)
¶
返回表示当前全局符号表的字典。这始终是当前模块的字典 (在函数或方法内，这是定义它的模块，而不是调用它的模块)。
hasattr
(
object
,
name
)
¶
自变量是对象和字符串。结果为
True
若字符串是对象某一属性的名称，
False
若不是。(这被实现通过调用
getattr(object,
name)
和看它是否引发
AttributeError
或不。)
hash
(
object
)
¶
Return the hash value of the object (if it has one). Hash values are integers. They are used to quickly compare dictionary keys during a dictionary lookup. Numeric values that compare equal have the same hash value (even if they are of different types, as is the case for 1 and 1.0).
注意
For objects with custom
__hash__()
methods, note that
hash()
truncates the return value based on the bit width of the host machine. See
__hash__()
了解细节。
help
(
[
object
]
)
¶
Invoke the built-in help system. (This function is intended for interactive use.) If no argument is given, the interactive help system starts on the interpreter console. If the argument is a string, then the string is looked up as the name of a module, function, class, method, keyword, or documentation topic, and a help page is printed on the console. If the argument is any other kind of object, a help page on the object is generated.
This function is added to the built-in namespace by the
site
模块。
hex
(
x
)
¶
Convert an integer number to a lowercase hexadecimal string prefixed with “0x”. If
x
is not a Python
int
object, it has to define an
__index__()
method that returns an integer. Some examples:
>>> hex(255)
'0xff'
>>> hex(-42)
'-0x2a'
If you want to convert an integer number to an uppercase or lower hexadecimal string with prefix or not, you can use either of the following ways:
>>> '%#x' % 255, '%x' % 255, '%X' % 255
('0xff', 'ff', 'FF')
>>> format(255, '#x'), format(255, 'x'), format(255, 'X')
('0xff', 'ff', 'FF')
>>> f'{255:#x}', f'{255:x}', f'{255:X}'
('0xff', 'ff', 'FF')
另请参阅
format()
了解更多信息。
另请参阅
int()
for converting a hexadecimal string to an integer using a base of 16.
注意
要获得浮点数的十六进制字符串表示，使用
float.hex()
方法。
id
(
object
)
¶
Return the “identity” of an object. This is an integer which is guaranteed to be unique and constant for this object during its lifetime. Two objects with non-overlapping lifetimes may have the same
id()
值。
CPython 实现细节： 这是对象在内存中的地址。
input
(
[
prompt
]
)
¶
若
prompt
argument is present, it is written to standard output without a trailing newline. The function then reads a line from input, converts it to a string (stripping a trailing newline), and returns that. When EOF is read,
EOFError
被引发。范例：
>>> s = input('--> ')
--> Monty Python's Flying Circus
>>> s
"Monty Python's Flying Circus"
int
(
x=0
)
¶
int
(
x
,
base=10
)
Return an integer object constructed from a number or string
x
, or return
0
if no arguments are given. If
x
定义
__int__()
,
int(x)
返回
x.__int__()
。若
x
定义
__trunc__()
，它返回
x.__trunc__()
. For floating point numbers, this truncates towards zero.
若
x
is not a number or if
base
is given, then
x
must be a string,
bytes
，或
bytearray
instance representing an
integer literal
in radix
base
. Optionally, the literal can be preceded by
+
or
-
(with no space in between) and surrounded by whitespace. A base-n literal consists of the digits 0 to n-1, with
a
to
z
(或
A
to
Z
) having values 10 to 35. The default
base
is 10. The allowed values are 0 and 2–36. Base-2, -8, and -16 literals can be optionally prefixed with
0b
/
0B
,
0o
/
0O
，或
0x
/
0X
, as with integer literals in code. Base 0 means to interpret exactly as a code literal, so that the actual base is 2, 8, 10, or 16, and so that
int('010',
0)
is not legal, while
int('010')
is, as well as
int('010',
8)
.
整数类型的描述在 数值类型 — int float complex .
3.4 版改变：
若
base
不是实例化的
int
和
base
object has a
base.__index__
method, that method is called to obtain an integer for the base. Previous versions used
base.__int__
而不是
base.__index__
.
3.6 版改变： 允许按代码文字下划线分组数字。
isinstance
(
object
,
classinfo
)
¶
返回 True 若
object
argument is an instance of the
classinfo
argument, or of a (direct, indirect or
virtual
) subclass thereof. If
object
is not an object of the given type, the function always returns false. If
classinfo
is a tuple of type objects (or recursively, other such tuples), return true if
object
is an instance of any of the types. If
classinfo
is not a type or tuple of types and such tuples, a
TypeError
异常被引发。
issubclass
(
class
,
classinfo
)
¶
返回 True 若
class
is a subclass (direct, indirect or
virtual
) of
classinfo
. A class is considered a subclass of itself.
classinfo
may be a tuple of class objects, in which case every entry in
classinfo
will be checked. In any other case, a
TypeError
异常被引发。
iter
(
object
[
,
sentinel
]
)
¶
返回
iterator
object. The first argument is interpreted very differently depending on the presence of the second argument. Without a second argument,
object
must be a collection object which supports the iteration protocol (the
__iter__()
method), or it must support the sequence protocol (the
__getitem__()
方法采用的整数自变量开始于
0
). If it does not support either of those protocols,
TypeError
is raised. If the second argument,
sentinel
, is given, then
object
must be a callable object. The iterator created in this case will call
object
with no arguments for each call to its
__next__()
method; if the value returned is equal to
sentinel
,
StopIteration
will be raised, otherwise the value will be returned.
另请参阅 迭代器类型 .
One useful application of the second form of
iter()
is to read lines of a file until a certain line is reached. The following example reads a file until the
readline()
method returns an empty string:
with open('mydata.txt') as fp:
for line in iter(fp.readline, ''):
process_line(line)
len
(
s
)
¶
Return the length (the number of items) of an object. The argument may be a sequence (such as a string, bytes, tuple, list, or range) or a collection (such as a dictionary, set, or frozen set).
list
(
[
iterable
]
)
除了是函数，
list
实际是可变序列类型，如文档化在
列表
and
序列类型 — list tuple range
.
locals
(
)
¶
更新并返回表示当前本地符号表的字典。自由变量的返回通过
locals()
当在函数块中而不是类块中调用它时。
注意
此词典的内容不应被修改；更改可能不影响由解释器使用的局部变量和自由变量的值。
map
(
function
,
iterable
,
...
)
¶
返回的迭代器应用
function
到每项为
iterable
，产生结果。若额外
iterable
arguments are passed,
function
must take that many arguments and is applied to the items from all iterables in parallel. With multiple iterables, the iterator stops when the shortest iterable is exhausted. For cases where the function inputs are already arranged into argument tuples, see
itertools.starmap()
.
max
(
iterable
,
*
[
,
key
,
default
]
)
¶
max
(
arg1
,
arg2
,
*args
[
,
key
]
)
Return the largest item in an iterable or the largest of two or more arguments.
If one positional argument is provided, it should be an iterable . The largest item in the iterable is returned. If two or more positional arguments are provided, the largest of the positional arguments is returned.
There are two optional keyword-only arguments. The
key
argument specifies a one-argument ordering function like that used for
list.sort()
。
default
argument specifies an object to return if the provided iterable is empty. If the iterable is empty and
default
is not provided, a
ValueError
被引发。
If multiple items are maximal, the function returns the first one encountered. This is consistent with other sort-stability preserving tools such as
sorted(iterable,
key=keyfunc,
reverse=True)[0]
and
heapq.nlargest(1,
iterable,
key=keyfunc)
.
3.4 版新增： default 仅关键词自变量。
memoryview
(
obj
)
返回从给定自变量创建的内存视图对象。见 内存视图 了解更多信息。
min
(
iterable
,
*
[
,
key
,
default
]
)
¶
min
(
arg1
,
arg2
,
*args
[
,
key
]
)
Return the smallest item in an iterable or the smallest of two or more arguments.
If one positional argument is provided, it should be an iterable . The smallest item in the iterable is returned. If two or more positional arguments are provided, the smallest of the positional arguments is returned.
There are two optional keyword-only arguments. The
key
argument specifies a one-argument ordering function like that used for
list.sort()
。
default
argument specifies an object to return if the provided iterable is empty. If the iterable is empty and
default
is not provided, a
ValueError
被引发。
If multiple items are minimal, the function returns the first one encountered. This is consistent with other sort-stability preserving tools such as
sorted(iterable,
key=keyfunc)[0]
and
heapq.nsmallest(1,
iterable,
key=keyfunc)
.
3.4 版新增： default 仅关键词自变量。
next
(
iterator
[
,
default
]
)
¶
Retrieve the next item from the
iterator
by calling its
__next__()
method. If
default
is given, it is returned if the iterator is exhausted, otherwise
StopIteration
被引发。
object
¶
返回新的无特征对象。
object
is a base for all classes. It has the methods that are common to all instances of Python classes. This function does not accept any arguments.
oct
(
x
)
¶
Convert an integer number to an octal string prefixed with “0o”. The result is a valid Python expression. If
x
is not a Python
int
object, it has to define an
__index__()
方法返回整数。例如：
>>> oct(8)
'0o10'
>>> oct(-56)
'-0o70'
If you want to convert an integer number to octal string either with prefix “0o” or not, you can use either of the following ways.
>>> '%#o' % 10, '%o' % 10
('0o12', '12')
>>> format(10, '#o'), format(10, 'o')
('0o12', '12')
>>> f'{10:#o}', f'{10:o}'
('0o12', '12')
另请参阅
format()
了解更多信息。
open
(
file
,
mode='r'
,
buffering=-1
,
encoding=None
,
errors=None
,
newline=None
,
closefd=True
,
opener=None
)
¶
打开
file
并返回相应
文件对象
。若文件不可以被打开，
OSError
被引发。
file
是
像路径对象
giving the pathname (absolute or relative to the current working directory) of the file to be opened or an integer file descriptor of the file to be wrapped. (If a file descriptor is given, it is closed when the returned I/O object is closed, unless
closefd
被设为
False
.)
mode
is an optional string that specifies the mode in which the file is opened. It defaults to
'r'
which means open for reading in text mode. Other common values are
'w'
for writing (truncating the file if it already exists),
'x'
for exclusive creation and
'a'
for appending (which on
some
Unix systems, means that
all
writes append to the end of the file regardless of the current seek position). In text mode, if
encoding
is not specified the encoding used is platform dependent:
locale.getpreferredencoding(False)
is called to get the current locale encoding. (For reading and writing raw bytes use binary mode and leave
encoding
unspecified.) The available modes are:
| 字符 | 含义 |
|---|---|
'r'
|
打开为读取 (默认) |
'w'
|
打开为写入，先截取文件 |
'x'
|
打开为独占创建，失败若文件已存在 |
'a'
|
打开为写入，追加到文件末尾若存在 |
'b'
|
二进制模式 |
't'
|
文本模式 (默认) |
'+'
|
打开磁盘文件为更新 (读写) |
'U'
|
通用换行符 模式 (弃用) |
默认模式为
'r'
(打开为读取文本，同义词
'rt'
)。对于二进制读写访问，模式
'w+b'
打开并截取文件到 0 字节。
'r+b'
打开文件不截断。
作为提及在
概述
, Python distinguishes between binary and text I/O. Files opened in binary mode (including
'b'
在
mode
argument) return contents as
bytes
objects without any decoding. In text mode (the default, or when
't'
is included in the
mode
argument), the contents of the file are returned as
str
, the bytes having been first decoded using a platform-dependent encoding or using the specified
encoding
if given.
注意
Python doesn’t depend on the underlying operating system’s notion of text files; all the processing is done by Python itself, and is therefore platform-independent.
buffering is an optional integer used to set the buffering policy. Pass 0 to switch buffering off (only allowed in binary mode), 1 to select line buffering (only usable in text mode), and an integer > 1 to indicate the size in bytes of a fixed-size chunk buffer. When no buffering argument is given, the default buffering policy works as follows:
io.DEFAULT_BUFFER_SIZE
. On many systems, the buffer will typically be 4096 or 8192 bytes long.
isatty()
返回
True
) use line buffering. Other text files use the policy described above for binary files.
encoding
is the name of the encoding used to decode or encode the file. This should only be used in text mode. The default encoding is platform dependent (whatever
locale.getpreferredencoding()
returns), but any
文本编码
supported by Python can be used. See the
codecs
模块，了解支持的编码列表。
errors
is an optional string that specifies how encoding and decoding errors are to be handled—this cannot be used in binary mode. A variety of standard error handlers are available (listed under
错误处理程序
), though any error handling name that has been registered with
codecs.register_error()
is also valid. The standard names include:
'strict'
to raise a
ValueError
exception if there is an encoding error. The default value of
None
has the same effect.
'ignore'
ignores errors. Note that ignoring encoding errors can lead to data loss.
'replace'
causes a replacement marker (such as
'?'
) to be inserted where there is malformed data.
'surrogateescape'
will represent any incorrect bytes as code points in the Unicode Private Use Area ranging from U+DC80 to U+DCFF. These private code points will then be turned back into the same bytes when the
surrogateescape
error handler is used when writing data. This is useful for processing files in an unknown encoding.
'xmlcharrefreplace'
is only supported when writing to a file. Characters not supported by the encoding are replaced with the appropriate XML character reference
&#nnn;
.
'backslashreplace'
replaces malformed data by Python’s backslashed escape sequences.
'namereplace'
(also only supported when writing) replaces unsupported characters with
\N{...}
escape sequences.
newline
控制如何
通用换行符
模式工作 (它仅应用于文本模式)。它可以为
None
,
''
,
'\n'
,
'\r'
，和
'\r\n'
. It works as follows:
None
, universal newlines mode is enabled. Lines in the input can end in
'\n'
,
'\r'
，或
'\r\n'
, and these are translated into
'\n'
before being returned to the caller. If it is
''
, universal newlines mode is enabled, but line endings are returned to the caller untranslated. If it has any of the other legal values, input lines are only terminated by the given string, and the line ending is returned to the caller untranslated.
None
, any
'\n'
characters written are translated to the system default line separator,
os.linesep
。若
newline
is
''
or
'\n'
, no translation takes place. If
newline
is any of the other legal values, any
'\n'
characters written are translated to the given string.
若
closefd
is
False
and a file descriptor rather than a filename was given, the underlying file descriptor will be kept open when the file is closed. If a filename is given
closefd
必须是
True
(the default) otherwise an error will be raised.
A custom opener can be used by passing a callable as
opener
. The underlying file descriptor for the file object is then obtained by calling
opener
with (
file
,
flags
).
opener
must return an open file descriptor (passing
os.open
as
opener
results in functionality similar to passing
None
).
新近创建的文件 不可继承 .
以下范例使用
dir_fd
parameter of the
os.open()
function to open a file relative to a given directory:
>>> import os
>>> dir_fd = os.open('somedir', os.O_RDONLY)
>>> def opener(path, flags):
... return os.open(path, flags, dir_fd=dir_fd)
...
>>> with open('spamspam.txt', 'w', opener=opener) as f:
... print('This will be written to somedir/spamspam.txt', file=f)
...
>>> os.close(dir_fd) # don't leak a file descriptor
The type of
文件对象
returned by the
open()
function depends on the mode. When
open()
is used to open a file in a text mode (
'w'
,
'r'
,
'wt'
,
'rt'
, etc.), it returns a subclass of
io.TextIOBase
(specifically
io.TextIOWrapper
). When used to open a file in a binary mode with buffering, the returned class is a subclass of
io.BufferedIOBase
. The exact class varies: in read binary mode, it returns an
io.BufferedReader
; in write binary and append binary modes, it returns an
io.BufferedWriter
, and in read/write mode, it returns an
io.BufferedRandom
. When buffering is disabled, the raw stream, a subclass of
io.RawIOBase
,
io.FileIO
, is returned.
See also the file handling modules, such as,
fileinput
,
io
(在哪里
open()
is declared),
os
,
os.path
,
tempfile
，和
shutil
.
3.3 版改变：
- opener 参数被添加。
'x'模式被添加。IOError用于被引发，它现在是别名化的OSError.FileExistsErroris now raised if the file opened in exclusive creation mode ('x') 已存在。
3.4 版改变：
- 文件现在不可继承。
从 3.4 版起弃用，将在 4.0 版中移除：
'U'
模式。
3.5 版改变：
- If the system call is interrupted and the signal handler does not raise an exception, the function now retries the system call instead of raising an
InterruptedError异常 (见 PEP 475 了解基本原理)。'namereplace'错误处理程序被添加。
3.6 版改变：
- Support added to accept objects implementing
os.PathLike.- On Windows, opening a console buffer may return a subclass of
io.RawIOBaseother thanio.FileIO.
ord
(
c
)
¶
给定表示一 Unicode 字符的字符串，返回整数表示该字符的 Unicode 代码点。例如，
ord('a')
返回整数
97
and
ord('€')
(欧元符号) 返回
8364
。这是逆对于
chr()
.
pow
(
x
,
y
[
,
z
]
)
¶
返回
x
to the power
y
; if
z
is present, return
x
to the power
y
, modulo
z
(computed more efficiently than
pow(x,
y)
%
z
). The two-argument form
pow(x,
y)
is equivalent to using the power operator:
x**y
.
The arguments must have numeric types. With mixed operand types, the coercion rules for binary arithmetic operators apply. For
int
operands, the result has the same type as the operands (after coercion) unless the second argument is negative; in that case, all arguments are converted to float and a float result is delivered. For example,
10**2
返回
100
，但
10**-2
返回
0.01
. If the second argument is negative, the third argument must be omitted. If
z
is present,
x
and
y
must be of integer types, and
y
must be non-negative.
print
(
*objects
,
sep=' '
,
end='\n'
,
file=sys.stdout
,
flush=False
)
¶
Print 对象 to the text stream file , separated by sep and followed by end . sep , end , file and flush , if present, must be given as keyword arguments.
All non-keyword arguments are converted to strings like
str()
does and written to the stream, separated by
sep
and followed by
end
. Both
sep
and
end
must be strings; they can also be
None
, which means to use the default values. If no
对象
are given,
print()
will just write
end
.
file
argument must be an object with a
write(string)
method; if it is not present or
None
,
sys.stdout
will be used. Since printed arguments are converted to text strings,
print()
cannot be used with binary mode file objects. For these, use
file.write(...)
代替。
Whether output is buffered is usually determined by file , but if the flush keyword argument is true, the stream is forcibly flushed.
3.3 版改变： 添加 flush 关键词自变量。
property
(
fget=None
,
fset=None
,
fdel=None
,
doc=None
)
¶
返回特性属性。
fget is a function for getting an attribute value. fset is a function for setting an attribute value. fdel is a function for deleting an attribute value. And doc creates a docstring for the attribute.
A typical use is to define a managed attribute
x
:
class C:
def __init__(self):
self._x = None
def getx(self):
return self._x
def setx(self, value):
self._x = value
def delx(self):
del self._x
x = property(getx, setx, delx, "I'm the 'x' property.")
若
c
是实例化的
C
,
c.x
will invoke the getter,
c.x
=
value
will invoke the setter and
del
c.x
the deleter.
若给定，
doc
will be the docstring of the property attribute. Otherwise, the property will copy
fget
’s docstring (if it exists). This makes it possible to create read-only properties easily using
property()
as a
装饰器
:
class Parrot:
def __init__(self):
self._voltage = 100000
@property
def voltage(self):
"""Get the current voltage."""
return self._voltage
@property
decorator turns the
voltage()
method into a “getter” for a read-only attribute with the same name, and it sets the docstring for
voltage
to “Get the current voltage.”
A property object has
getter
,
setter
，和
deleter
methods usable as decorators that create a copy of the property with the corresponding accessor function set to the decorated function. This is best explained with an example:
class C:
def __init__(self):
self._x = None
@property
def x(self):
"""I'm the 'x' property."""
return self._x
@x.setter
def x(self, value):
self._x = value
@x.deleter
def x(self):
del self._x
This code is exactly equivalent to the first example. Be sure to give the additional functions the same name as the original property (
x
in this case.)
The returned property object also has the attributes
fget
,
fset
，和
fdel
corresponding to the constructor arguments.
3.5 版改变： The docstrings of property objects are now writeable.
range
(
stop
)
range
(
start
,
stop
[
,
step
]
)
除了是函数，
range
is actually an immutable sequence type, as documented in
Ranges
and
序列类型 — list tuple range
.
repr
(
object
)
¶
Return a string containing a printable representation of an object. For many types, this function makes an attempt to return a string that would yield an object with the same value when passed to
eval()
, otherwise the representation is a string enclosed in angle brackets that contains the name of the type of the object together with additional information often including the name and address of the object. A class can control what this function returns for its instances by defining a
__repr__()
方法。
reversed
(
seq
)
¶
返回反向
iterator
.
seq
必须是对象且有
__reversed__()
方法或支持序列协议 (
__len__()
方法和
__getitem__()
方法采用的整数自变量开始于
0
).
round
(
number
[
,
ndigits
]
)
¶
返回
number
四舍五入到
ndigits
精度在小数点之后。若
ndigits
被省略或为
None
，它返回最接近输入的整数。
对于内置类型支持
round()
，值被四舍五入到最接近 10 的倍数的乘幂
ndigits
；若 2 个倍数接近相等，朝偶数选择完成四舍五入 (因此，例如
round(0.5)
and
round(-0.5)
are
0
，和
round(1.5)
is
2
)。任何整数值有效对于
ndigits
(正数、零或负数)。返回值是整数若
ndigits
被省略或
None
。否则，返回值拥有相同类型如
number
.
对于一般 Python 对象
number
,
round
委托
number.__round__
.
注意
行为在
round()
对于浮点数可能出人意料：例如，
round(2.675,
2)
给出
2.67
而不是期望的
2.68
。这不是 Bug：事实是大多数十进制小数不能准确表示成浮点的结果。见
浮点算术：问题和局限性
了解更多信息。
set
(
[
iterable
]
)
返回新
set
object, optionally with elements taken from
iterable
.
set
is a built-in class. See
set
and
Set Types — set, frozenset
有关此类的文档编制。
对于其它容器，见内置
frozenset
,
list
,
tuple
，和
dict
类，及
collections
模块。
setattr
(
object
,
name
,
value
)
¶
这搭档
getattr()
。自变量是对象、字符串和任意值。字符串可以命名现有属性或新属性。函数将值赋值给属性，若提供对象允许。例如，
setattr(x,
'foobar',
123)
相当于
x.foobar
=
123
.
slice
(
stop
)
¶
slice
(
start
,
stop
[
,
step
]
)
返回
slice
object representing the set of indices specified by
range(start,
stop,
step)
。
start
and
step
arguments default to
None
. Slice objects have read-only data attributes
start
,
stop
and
step
which merely return the argument values (or their default). They have no other explicit functionality; however they are used by Numerical Python and other third party extensions. Slice objects are also generated when extended indexing syntax is used. For example:
a[start:stop:step]
or
a[start:stop,
i]
。见
itertools.islice()
for an alternate version that returns an iterator.
sorted
(
iterable
,
*
,
key=None
,
reverse=False
)
¶
返回新的排序列表项来自 iterable .
拥有 2 个必须被指定为关键字自变量的可选自变量。
key
specifies a function of one argument that is used to extract a comparison key from each element in
iterable
(for example,
key=str.lower
). The default value is
None
(compare the elements directly).
reverse
is a boolean value. If set to
True
, then the list elements are sorted as if each comparison were reversed.
使用
functools.cmp_to_key()
to convert an old-style
cmp
function to a
key
函数。
内置
sorted()
function 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).
For sorting examples and a brief sorting tutorial, see Sorting HOW TO .
@
staticmethod
¶
将方法变换成静态方法。
A static method does not receive an implicit first argument. To declare a static method, use this idiom:
class C:
@staticmethod
def f(arg1, arg2, ...): ...
@staticmethod
形式是函数
装饰器
– 见函数定义描述在
函数定义
了解细节。
It can be called either on the class (such as
C.f()
) or on an instance (such as
C().f()
). The instance is ignored except for its class.
Static methods in Python are similar to those found in Java or C++. Also see
classmethod()
for a variant that is useful for creating alternate class constructors.
Like all decorators, it is also possible to call
staticmethod
as a regular function and do something with its result. This is needed in some cases where you need a reference to a function from a class body and you want to avoid the automatic transformation to instance method. For these cases, use this idiom:
class C:
builtin_open = staticmethod(open)
For more information on static methods, consult the documentation on the standard type hierarchy in 标准类型层次结构 .
str
(
object=''
)
str
(
object=b''
,
encoding='utf-8'
,
errors='strict'
)
返回
str
版本的
object
。见
str()
了解细节。
str
是内置字符串
class
。有关字符串的一般信息，见
文本序列类型 — str
.
sum
(
iterable
[
,
start
]
)
¶
求和
start
and the items of an
iterable
from left to right and returns the total.
start
默认为
0
。
iterable
的项通常是数字，且 start 值不允许是字符串。
For some use cases, there are good alternatives to
sum()
. The preferred, fast way to concatenate a sequence of strings is by calling
''.join(sequence)
. To add floating point values with extended precision, see
math.fsum()
. To concatenate a series of iterables, consider using
itertools.chain()
.
super
(
[
type
[
,
object-or-type
]
]
)
¶
Return a proxy object that delegates method calls to a parent or sibling class of
type
. This is useful for accessing inherited methods that have been overridden in a class. The search order is same as that used by
getattr()
except that the
type
itself is skipped.
__mro__
属性在
type
lists the method resolution search order used by both
getattr()
and
super()
. The attribute is dynamic and can change whenever the inheritance hierarchy is updated.
If the second argument is omitted, the super object returned is unbound. If the second argument is an object,
isinstance(obj,
type)
must be true. If the second argument is a type,
issubclass(type2,
type)
must be true (this is useful for classmethods).
There are two typical use cases for super . In a class hierarchy with single inheritance, super can be used to refer to parent classes without naming them explicitly, thus making the code more maintainable. This use closely parallels the use of super in other programming languages.
The second use case is to support cooperative multiple inheritance in a dynamic execution environment. This use case is unique to Python and is not found in statically compiled languages or languages that only support single inheritance. This makes it possible to implement “diamond diagrams” where multiple base classes implement the same method. Good design dictates that this method have the same calling signature in every case (because the order of calls is determined at runtime, because that order adapts to changes in the class hierarchy, and because that order can include sibling classes that are unknown prior to runtime).
For both use cases, a typical superclass call looks like this:
class C(B):
def method(self, arg):
super().method(arg) # This does the same thing as:
# super(C, self).method(arg)
注意，
super()
is implemented as part of the binding process for explicit dotted attribute lookups such as
super().__getitem__(name)
. It does so by implementing its own
__getattribute__()
method for searching classes in a predictable order that supports cooperative multiple inheritance. Accordingly,
super()
is undefined for implicit lookups using statements or operators such as
super()[name]
.
Also note that, aside from the zero argument form,
super()
is not limited to use inside methods. The two argument form specifies the arguments exactly and makes the appropriate references. The zero argument form only works inside a class definition, as the compiler fills in the necessary details to correctly retrieve the class being defined, as well as accessing the current instance for ordinary methods.
For practical suggestions on how to design cooperative classes using
super()
，见
guide to using super()
.
tuple
(
[
iterable
]
)
除了是函数，
tuple
is actually an immutable sequence type, as documented in
元组
and
序列类型 — list tuple range
.
type
(
object
)
¶
type
(
name
,
bases
,
dict
)
With one argument, return the type of an
object
. The return value is a type object and generally the same object as returned by
object.__class__
.
isinstance()
built-in function is recommended for testing the type of an object, because it takes subclasses into account.
With three arguments, return a new type object. This is essentially a dynamic form of the
class
statement. The
name
string is the class name and becomes the
__name__
attribute; the
bases
tuple itemizes the base classes and becomes the
__bases__
attribute; and the
dict
dictionary is the namespace containing definitions for class body and is copied to a standard dictionary to become the
__dict__
attribute. For example, the following two statements create identical
type
对象：
>>> class X:
... a = 1
...
>>> X = type('X', (object,), dict(a=1))
另请参阅 类型对象 .
3.6 版改变：
子类化的
type
which don’t override
type.__new__
may no longer use the one-argument form to get the type of an object.
vars
(
[
object
]
)
¶
返回
__dict__
attribute for a module, class, instance, or any other object with a
__dict__
属性。
Objects such as modules and instances have an updateable
__dict__
attribute; however, other objects may have write restrictions on their
__dict__
attributes (for example, classes use a
types.MappingProxyType
to prevent direct dictionary updates).
没有自变量，
vars()
举动像
locals()
. Note, the locals dictionary is only useful for reads since updates to the locals dictionary are ignored.
zip
(
*iterables
)
¶
制作聚合每个可迭代元素的迭代器。
Returns an iterator of tuples, where the i -th tuple contains the i -th element from each of the argument sequences or iterables. The iterator stops when the shortest input iterable is exhausted. With a single iterable argument, it returns an iterator of 1-tuples. With no arguments, it returns an empty iterator. Equivalent to:
def zip(*iterables):
# zip('ABCD', 'xy') --> Ax By
sentinel = object()
iterators = [iter(it) for it in iterables]
while iterators:
result = []
for it in iterators:
elem = next(it, sentinel)
if elem is sentinel:
return
result.append(elem)
yield tuple(result)
The left-to-right evaluation order of the iterables is guaranteed. This makes possible an idiom for clustering a data series into n-length groups using
zip(*[iter(s)]*n)
. This repeats the
same
iterator
n
times so that each output tuple has the result of
n
calls to the iterator. This has the effect of dividing the input into n-length chunks.
zip()
should only be used with unequal length inputs when you don’t care about trailing, unmatched values from the longer iterables. If those values are important, use
itertools.zip_longest()
代替。
zip()
in conjunction with the
*
operator can be used to unzip a list:
>>> x = [1, 2, 3]
>>> y = [4, 5, 6]
>>> zipped = zip(x, y)
>>> list(zipped)
[(1, 4), (2, 5), (3, 6)]
>>> x2, y2 = zip(*zip(x, y))
>>> x == list(x2) and y == list(y2)
True
__import__
(
name
,
globals=None
,
locals=None
,
fromlist=()
,
level=0
)
¶
注意
This is an advanced function that is not needed in everyday Python programming, unlike
importlib.import_module()
.
This function is invoked by the
import
statement. It can be replaced (by importing the
builtins
module and assigning to
builtins.__import__
) in order to change semantics of the
import
statement, but doing so is
strongly
discouraged as it is usually simpler to use import hooks (see
PEP 302
) to attain the same goals and does not cause issues with code which assumes the default import implementation is in use. Direct use of
__import__()
is also discouraged in favor of
importlib.import_module()
.
The function imports the module
name
, potentially using the given
globals
and
locals
to determine how to interpret the name in a package context.
fromlist
gives the names of objects or submodules that should be imported from the module given by
name
. The standard implementation does not use its
locals
argument at all, and uses its
globals
only to determine the package context of the
import
语句。
level
specifies whether to use absolute or relative imports.
0
(the default) means only perform absolute imports. Positive values for
level
indicate the number of parent directories to search relative to the directory of the module calling
__import__()
(见
PEP 328
for the details).
当
name
variable is of the form
package.module
, normally, the top-level package (the name up till the first dot) is returned,
not
the module named by
name
. However, when a non-empty
fromlist
argument is given, the module named by
name
被返回。
For example, the statement
import
spam
results in bytecode resembling the following code:
spam = __import__('spam', globals(), locals(), [], 0)
The statement
import
spam.ham
results in this call:
spam = __import__('spam.ham', globals(), locals(), [], 0)
Note how
__import__()
returns the toplevel module here because this is the object that is bound to a name by the
import
语句。
On the other hand, the statement
from
spam.ham
import
eggs,
sausage
as
saus
results in
_temp = __import__('spam.ham', globals(), locals(), ['eggs', 'sausage'], 0)
eggs = _temp.eggs
saus = _temp.sausage
在这里，
spam.ham
module is returned from
__import__()
. From this object, the names to import are retrieved and assigned to their respective names.
If you simply want to import a module (potentially within a package) by name, use
importlib.import_module()
.
3.3 版改变： 负值 level are no longer supported (which also changes the default value to 0).
脚注
| [1] | Note that the parser only accepts the Unix-style end of line convention. If you are reading the code from a file, make sure to use newline conversion mode to convert Windows or Mac-style newlines. |