A Python program is read by a parser . Input to the parser is a stream of tokens , generated by the 词法分析器 . This chapter describes how the lexical analyzer breaks a file into tokens.
Python reads program text as Unicode code points; the encoding of a source file can be given by an encoding declaration and defaults to UTF-8, see
PEP 3120
for details. If the source file cannot be decoded, a
SyntaxError
被引发。
Python 程序被分成许多 逻辑行 .
The end of a logical line is represented by the token NEWLINE. Statements cannot cross logical line boundaries except where NEWLINE is allowed by the syntax (e.g., between statements in compound statements). A logical line is constructed from one or more physical lines by following the explicit or implicit 行联接 规则。
A physical line is a sequence of characters terminated by an end-of-line sequence. In source files and strings, any of the standard platform line termination sequences can be used - the Unix form using ASCII LF (linefeed), the Windows form using the ASCII sequence CR LF (return followed by linefeed), or the old Macintosh form using the ASCII CR (return) character. All of these forms can be used equally, regardless of platform. The end of input also serves as an implicit terminator for the final physical line.
When embedding Python, source code strings should be passed to Python APIs using the standard C conventions for newline characters (the
\n
character, representing ASCII LF, is the line terminator).
注释开头的哈希字符 (
#
) that is not part of a string literal, and ends at the end of the physical line. A comment signifies the end of the logical line unless the implicit line joining rules are invoked. Comments are ignored by the syntax.
若 Python 脚本第 1 (或第 2) 行注释匹配正则表达式
coding[=:]\s*([-\w.]+)
，将作为编码声明处理此注释；表达式的第 1 组命名源代码文件的编码。编码声明必须单独出现在一行中。若编码声明在第 2 行，第 1 行也必须是仅注释行。推荐的编码表达式形式
# -*- coding: <encoding-name> -*-
其也被 GNU Emacs 认可，而
# vim:fileencoding=<encoding-name>
其由 Bram Moolenaar 的 VIM 认可。
若未找到编码声明，默认编码为 UTF-8。此外，若文件的第 1 字节为 UTF-8 字节序标记 (
b'\xef\xbb\xbf'
)，声明的文件编码为 UTF-8 (除其它外，这被支持由微软的
notepad
).
If an encoding is declared, the encoding name must be recognized by Python (see 标准编码 ). The encoding is used for all lexical analysis, including string literals, comments and identifiers.
Two or more physical lines may be joined into logical lines using backslash characters (
\
), as follows: when a physical line ends in a backslash that is not part of a string literal or comment, it is joined with the following forming a single logical line, deleting the backslash and the following end-of-line character. For example:
if 1900 < year < 2100 and 1 <= month <= 12 \ and 1 <= day <= 31 and 0 <= hour < 24 \ and 0 <= minute < 60 and 0 <= second < 60: # Looks like a valid date return 1
A line ending in a backslash cannot carry a comment. A backslash does not continue a comment. A backslash does not continue a token except for string literals (i.e., tokens other than string literals cannot be split across physical lines using a backslash). A backslash is illegal elsewhere on a line outside a string literal.
Expressions in parentheses, square brackets or curly braces can be split over more than one physical line without using backslashes. For example:
month_names = ['Januari', 'Februari', 'Maart', # These are the 'April', 'Mei', 'Juni', # Dutch names 'Juli', 'Augustus', 'September', # for the months 'Oktober', 'November', 'December'] # of the year
Implicitly continued lines can carry comments. The indentation of the continuation lines is not important. Blank continuation lines are allowed. There is no NEWLINE token between implicit continuation lines. Implicitly continued lines can also occur within triple-quoted strings (see below); in that case they cannot carry comments.
A logical line that contains only spaces, tabs, formfeeds and possibly a comment, is ignored (i.e., no NEWLINE token is generated). During interactive input of statements, handling of a blank line may differ depending on the implementation of the read-eval-print loop. In the standard interactive interpreter, an entirely blank logical line (i.e. one containing not even whitespace or a comment) terminates a multi-line statement.
Leading whitespace (spaces and tabs) at the beginning of a logical line is used to compute the indentation level of the line, which in turn is used to determine the grouping of statements.
Tabs are replaced (from left to right) by one to eight spaces such that the total number of characters up to and including the replacement is a multiple of eight (this is intended to be the same rule as used by Unix). The total number of spaces preceding the first non-blank character then determines the line’s indentation. Indentation cannot be split over multiple physical lines using backslashes; the whitespace up to the first backslash determines the indentation.
Indentation is rejected as inconsistent if a source file mixes tabs and spaces in a way that makes the meaning dependent on the worth of a tab in spaces; a
TabError
is raised in that case.
跨平台兼容性说明： because of the nature of text editors on non-UNIX platforms, it is unwise to use a mixture of spaces and tabs for the indentation in a single source file. It should also be noted that different platforms may explicitly limit the maximum indentation level.
A formfeed character may be present at the start of the line; it will be ignored for the indentation calculations above. Formfeed characters occurring elsewhere in the leading whitespace have an undefined effect (for instance, they may reset the space count to zero).
The indentation levels of consecutive lines are used to generate INDENT and DEDENT tokens, using a stack, as follows.
Before the first line of the file is read, a single zero is pushed on the stack; this will never be popped off again. The numbers pushed on the stack will always be strictly increasing from bottom to top. At the beginning of each logical line, the line’s indentation level is compared to the top of the stack. If it is equal, nothing happens. If it is larger, it is pushed on the stack, and one INDENT token is generated. If it is smaller, it must be one of the numbers occurring on the stack; all numbers on the stack that are larger are popped off, and for each number popped off a DEDENT token is generated. At the end of the file, a DEDENT token is generated for each number remaining on the stack that is larger than zero.
Here is an example of a correctly (though confusingly) indented piece of Python code:
def perm(l): # Compute the list of all permutations of l if len(l) <= 1: return [l] r = [] for i in range(len(l)): s = l[:i] + l[i+1:] p = perm(s) for x in p: r.append(l[i:i+1] + x) return r
The following example shows various indentation errors:
def perm(l): # error: first line indented for i in range(len(l)): # error: not indented s = l[:i] + l[i+1:] p = perm(l[:i] + l[i+1:]) # error: unexpected indent for x in p: r.append(l[i:i+1] + x) return r # error: inconsistent dedent
(Actually, the first three errors are detected by the parser; only the last error is found by the lexical analyzer — the indentation of
return r
does not match a level popped off the stack.)
Except at the beginning of a logical line or in string literals, the whitespace characters space, tab and formfeed can be used interchangeably to separate tokens. Whitespace is needed between two tokens only if their concatenation could otherwise be interpreted as a different token (e.g., ab is one token, but a b is two tokens).
Besides NEWLINE, INDENT and DEDENT, the following categories of tokens exist: identifiers , keywords , literals , operators ，和 delimiters . Whitespace characters (other than line terminators, discussed earlier) are not tokens, but serve to delimit tokens. Where ambiguity exists, a token comprises the longest possible string that forms a legal token, when read from left to right.
标识符(也称为 名称 ) are described by the following lexical definitions.
The syntax of identifiers in Python is based on the Unicode standard annex UAX-31, with elaboration and changes as defined below; see also PEP 3131 进一步了解细节。
Within the ASCII range (U+0001..U+007F), the valid characters for identifiers are the same as in Python 2.x: the uppercase and lowercase letters
A
through
Z
, the underscore
_
and, except for the first character, the digits
0
through
9
.
Python 3.0 introduces additional characters from outside the ASCII range (see
PEP 3131
). For these characters, the classification uses the version of the Unicode Character Database as included in the
unicodedata
模块。
Identifiers are unlimited in length. Case is significant.
identifier ::=xid_startxid_continue* id_start ::= <all characters in general categories Lu, Ll, Lt, Lm, Lo, Nl, the underscore, and characters with the Other_ID_Start property> id_continue ::= <all characters inid_start, plus characters in the categories Mn, Mc, Nd, Pc and others with the Other_ID_Continue property> xid_start ::= <all characters inid_startwhose NFKC normalization is in "id_start xid_continue*"> xid_continue ::= <all characters inid_continuewhose NFKC normalization is in "id_continue*">
The Unicode category codes mentioned above stand for:
Lu - 大写字母
Ll - 小写字母
Lt - 标题大小写字母
Lm - 修饰符字母
Lo - 其它字母
Nl - 字母数字
Mn - 非间距标记
Mc - 间距组合标记
Nd - 十进制数字
Pc - 连接符标点
Other_ID_Start - 明确字符列表在 PropList.txt 以支持向后兼容
Other_ID_Continue - 同上
All identifiers are converted into the normal form NFKC while parsing; comparison of identifiers is based on NFKC.
A non-normative HTML file listing all valid identifier characters for Unicode 14.0.0 can be found at https://www.unicode.org/Public/14.0.0/ucd/DerivedCoreProperties.txt
The following identifiers are used as reserved words, or keywords of the language, and cannot be used as ordinary identifiers. They must be spelled exactly as written here:
False await else import pass None break except in raise True class finally is return and continue for lambda try as def from nonlocal while assert del global not with async elif if or yield
3.10 版新增。
Some identifiers are only reserved under specific contexts. These are known as
soft keywords
. The identifiers
match
,
case
and
_
can syntactically act as keywords in contexts related to the pattern matching statement, but this distinction is done at the parser level, not when tokenizing.
As soft keywords, their use with pattern matching is possible while still preserving compatibility with existing code that uses
match
,
case
and
_
as identifier names.
Certain classes of identifiers (besides keywords) have special meanings. These classes are identified by the patterns of leading and trailing underscore characters:
_*
Not imported by
from module import *
.
_
在
case
pattern within a
match
statement,
_
是
soft keyword
that denotes a
wildcard
.
Separately, the interactive interpreter makes the result of the last evaluation available in the variable
_
. (It is stored in the
builtins
module, alongside built-in functions like
print
)。
Elsewhere,
_
is a regular identifier. It is often used to name “special” items, but it is not special to Python itself.
注意
名称
_
is often used in conjunction with internationalization; refer to the documentation for the
gettext
module for more information on this convention.
It is also commonly used for unused variables.
__*__
System-defined names, informally known as “dunder” names. These names are defined by the interpreter and its implementation (including the standard library). Current system names are discussed in the
特殊方法名称
section and elsewhere. More will likely be defined in future versions of Python.
任何
use of
__*__
names, in any context, that does not follow explicitly documented use, is subject to breakage without warning.
__*
Class-private names. Names in this category, when used within the context of a class definition, are re-written to use a mangled form to help avoid name clashes between “private” attributes of base and derived classes. See section 标识符 (名称) .
文字是某些内置类型的常量值的表示法。
字符串文字由以下词法定义描述：
stringliteral ::= [stringprefix](shortstring|longstring) stringprefix ::= "r" | "u" | "R" | "U" | "f" | "F" | "fr" | "Fr" | "fR" | "FR" | "rf" | "rF" | "Rf" | "RF" shortstring ::= "'"shortstringitem* "'" | '"'shortstringitem* '"' longstring ::= "'''"longstringitem* "'''" | '"""'longstringitem* '"""' shortstringitem ::=shortstringchar|stringescapeseqlongstringitem ::=longstringchar|stringescapeseqshortstringchar ::= <any source character except "\" or newline or the quote> longstringchar ::= <any source character except "\"> stringescapeseq ::= "\" <any source character>
bytesliteral ::=bytesprefix(shortbytes|longbytes) bytesprefix ::= "b" | "B" | "br" | "Br" | "bR" | "BR" | "rb" | "rB" | "Rb" | "RB" shortbytes ::= "'"shortbytesitem* "'" | '"'shortbytesitem* '"' longbytes ::= "'''"longbytesitem* "'''" | '"""'longbytesitem* '"""' shortbytesitem ::=shortbyteschar|bytesescapeseqlongbytesitem ::=longbyteschar|bytesescapeseqshortbyteschar ::= <any ASCII character except "\" or newline or the quote> longbyteschar ::= <any ASCII character except "\"> bytesescapeseq ::= "\" <any ASCII character>
One syntactic restriction not indicated by these productions is that whitespace is not allowed between the
stringprefix
or
bytesprefix
and the rest of the literal. The source character set is defined by the encoding declaration; it is UTF-8 if no encoding declaration is given in the source file; see section
编码声明
.
In plain English: Both types of literals can be enclosed in matching single quotes (
'
) 或双引号 (
"
). They can also be enclosed in matching groups of three single or double quotes (these are generally referred to as
triple-quoted strings
). The backslash (
\
) character is used to escape characters that otherwise have a special meaning, such as newline, backslash itself, or the quote character.
Bytes literals are always prefixed with
'b'
or
'B'
; they produce an instance of the
bytes
type instead of the
str
type. They may only contain ASCII characters; bytes with a numeric value of 128 or greater must be expressed with escapes.
Both string and bytes literals may optionally be prefixed with a letter
'r'
or
'R'
; such strings are called
raw strings
and treat backslashes as literal characters. As a result, in string literals,
'\U'
and
'\u'
escapes in raw strings are not treated specially. Given that Python 2.x’s raw unicode literals behave differently than Python 3.x’s the
'ur'
syntax is not supported.
3.3 版新增：
'rb'
prefix of raw bytes literals has been added as a synonym of
'br'
.
3.3 版新增：
Support for the unicode legacy literal (
u'value'
) was reintroduced to simplify the maintenance of dual Python 2.x and 3.x codebases. See
PEP 414
了解更多信息。
字符串文字采用
'f'
or
'F'
在其前缀中是
格式化字符串文字
；见
格式化字符串文字
。
'f'
可以组合
'r'
，但不采用
'b'
or
'u'
，因此，原生格式化字符串是可能的，但格式化字节文字是不可能的。
In triple-quoted literals, unescaped newlines and quotes are allowed (and are retained), except that three unescaped quotes in a row terminate the literal. (A “quote” is the character used to open the literal, i.e. either
'
or
"
)。
除非
'r'
or
'R'
prefix is present, escape sequences in string and bytes literals are interpreted according to rules similar to those used by Standard C. The recognized escape sequences are:
| 转义序列 | 含义 | 注意事项 |
|---|---|---|
\
<newline>
|
反斜杠和换行符被忽略 | (1) |
\\
|
反斜杠 (
\
)
|
|
\'
|
单引号 (
'
)
|
|
\"
|
双引号 (
"
)
|
|
\a
|
ASCII 响铃 (BEL) | |
\b
|
ASCII 退格 (BS) | |
\f
|
ASCII 换页 (FF) | |
\n
|
ASCII 换行 (LF) | |
\r
|
ASCII CR (回车) | |
\t
|
ASCII 水平制表符 (TAB) | |
\v
|
ASCII 垂直制表符 (VT) | |
\ooo
|
字符具有八进制值 ooo | (2,4) |
\xhh
|
字符具有十六进制值 hh | (3,4) |
Escape sequences only recognized in string literals are:
| 转义序列 | 含义 | 注意事项 |
|---|---|---|
\N{name}
|
字符命名 name 在 Unicode 数据库中 | (5) |
\uxxxx
|
字符具有 16 位十六进制值 xxxx | (6) |
\Uxxxxxxxx
|
字符具有 32 位十六进制值 xxxxxxxx | (7) |
注意事项：
A backslash can be added at the end of a line to ignore the newline:
>>> 'This string will not include \ ... backslashes or newline characters.' 'This string will not include backslashes or newline characters.'
The same result can be achieved using triple-quoted strings , or parentheses and string literal concatenation .
As in Standard C, up to three octal digits are accepted.
3.11 版改变：
Octal escapes with value larger than
0o377
produce a
DeprecationWarning
. In a future Python version they will be a
SyntaxWarning
and eventually a
SyntaxError
.
Unlike in Standard C, exactly two hex digits are required.
In a bytes literal, hexadecimal and octal escapes denote the byte with the given value. In a string literal, these escapes denote a Unicode character with the given value.
3.3 版改变： Support for name aliases 1 has been added.
Exactly four hex digits are required.
Any Unicode character can be encoded this way. Exactly eight hex digits are required.
Unlike Standard C, all unrecognized escape sequences are left in the string unchanged, i.e., the backslash is left in the result . (This behavior is useful when debugging: if an escape sequence is mistyped, the resulting output is more easily recognized as broken.) It is also important to note that the escape sequences only recognized in string literals fall into the category of unrecognized escapes for bytes literals.
3.6 版改变：
Unrecognized escape sequences produce a
DeprecationWarning
. In a future Python version they will be a
SyntaxWarning
and eventually a
SyntaxError
.
Even in a raw literal, quotes can be escaped with a backslash, but the backslash remains in the result; for example,
r"\""
is a valid string literal consisting of two characters: a backslash and a double quote;
r"\"
is not a valid string literal (even a raw string cannot end in an odd number of backslashes). Specifically,
a raw literal cannot end in a single backslash
(since the backslash would escape the following quote character). Note also that a single backslash followed by a newline is interpreted as those two characters as part of the literal,
not
as a line continuation.
Multiple adjacent string or bytes literals (delimited by whitespace), possibly using different quoting conventions, are allowed, and their meaning is the same as their concatenation. Thus,
"hello" 'world'
相当于
"helloworld"
. This feature can be used to reduce the number of backslashes needed, to split long strings conveniently across long lines, or even to add comments to parts of strings, for example:
re.compile("[A-Za-z_]" # letter or underscore "[A-Za-z0-9_]*" # letter, digit or underscore )
Note that this feature is defined at the syntactical level, but implemented at compile time. The ‘+’ operator must be used to concatenate string expressions at run time. Also note that literal concatenation can use different quoting styles for each component (even mixing raw strings and triple quoted strings), and formatted string literals may be concatenated with plain string literals.
3.6 版新增。
A
格式化字符串文字
or
f-string
是加前缀的字符串文字采用
'f'
or
'F'
. These strings may contain replacement fields, which are expressions delimited by curly braces
{}
. While other string literals always have a constant value, formatted strings are really expressions evaluated at run time.
Escape sequences are decoded like in ordinary string literals (except when a literal is also marked as a raw string). After decoding, the grammar for the contents of the string is:
f_string ::= (literal_char| "{{" | "}}" |replacement_field)* replacement_field ::= "{"f_expression["="] ["!"conversion] [":"format_spec] "}" f_expression ::= (conditional_expression| "*"or_expr) (","conditional_expression| "," "*"or_expr)* [","] |yield_expressionconversion ::= "s" | "r" | "a" format_spec ::= (literal_char| NULL |replacement_field)* literal_char ::= <any code point except "{", "}" or NULL>
The parts of the string outside curly braces are treated literally, except that any doubled curly braces
'{{'
or
'}}'
are replaced with the corresponding single curly brace. A single opening curly bracket
'{'
marks a replacement field, which starts with a Python expression. To display both the expression text and its value after evaluation, (useful in debugging), an equal sign
'='
may be added after the expression. A conversion field, introduced by an exclamation point
'!'
may follow. A format specifier may also be appended, introduced by a colon
':'
. A replacement field ends with a closing curly bracket
'}'
.
Expressions in formatted string literals are treated like regular Python expressions surrounded by parentheses, with a few exceptions. An empty expression is not allowed, and both
lambda
and assignment expressions
:=
must be surrounded by explicit parentheses. Replacement expressions can contain line breaks (e.g. in triple-quoted strings), but they cannot contain comments. Each expression is evaluated in the context where the formatted string literal appears, in order from left to right.
3.7 版改变：
Prior to Python 3.7, an
await
expression and comprehensions containing an
async for
clause were illegal in the expressions in formatted string literals due to a problem with the implementation.
当等号
'='
is provided, the output will have the expression text, the
'='
and the evaluated value. Spaces after the opening brace
'{'
, within the expression and after the
'='
are all retained in the output. By default, the
'='
causes the
repr()
of the expression to be provided, unless there is a format specified. When a format is specified it defaults to the
str()
of the expression unless a conversion
'!r'
is declared.
3.8 版新增：
等号
'='
.
If a conversion is specified, the result of evaluating the expression is converted before formatting. Conversion
'!s'
调用
str()
on the result,
'!r'
调用
repr()
，和
'!a'
调用
ascii()
.
The result is then formatted using the
format()
protocol. The format specifier is passed to the
__format__()
method of the expression or conversion result. An empty string is passed when the format specifier is omitted. The formatted result is then included in the final value of the whole string.
Top-level format specifiers may include nested replacement fields. These nested fields may include their own conversion fields and
格式说明符
, but may not include more deeply nested replacement fields. The
格式说明符迷你语言
is the same as that used by the
str.format()
方法。
Formatted string literals may be concatenated, but replacement fields cannot be split across literals.
格式化字符串文字的一些范例：
>>> name = "Fred" >>> f"He said his name is {name!r}." "He said his name is 'Fred'." >>> f"He said his name is {repr(name)}." # repr() is equivalent to !r "He said his name is 'Fred'." >>> width = 10 >>> precision = 4 >>> value = decimal.Decimal("12.34567") >>> f"result: {value:{width}.{precision}}" # nested fields 'result: 12.35' >>> today = datetime(year=2017, month=1, day=27) >>> f"{today:%B %d, %Y}" # using date format specifier 'January 27, 2017' >>> f"{today=:%B %d, %Y}" # using date format specifier and debugging 'today=January 27, 2017' >>> number = 1024 >>> f"{number:#0x}" # using integer format specifier '0x400' >>> foo = "bar" >>> f"{ foo = }" # preserves whitespace " foo = 'bar'" >>> line = "The mill's closed" >>> f"{line = }" 'line = "The mill\'s closed"' >>> f"{line = :20}" "line = The mill's closed " >>> f"{line = !r:20}" 'line = "The mill\'s closed" '
A consequence of sharing the same syntax as regular string literals is that characters in the replacement fields must not conflict with the quoting used in the outer formatted string literal:
f"abc {a["x"]} def" # error: outer string literal ended prematurely f"abc {a['x']} def" # workaround: use different quoting
Backslashes are not allowed in format expressions and will raise an error:
f"newline: {ord('\n')}" # raises SyntaxError
To include a value in which a backslash escape is required, create a temporary variable.
>>> newline = ord('\n') >>> f"newline: {newline}" 'newline: 10'
Formatted string literals cannot be used as docstrings, even if they do not include expressions.
>>> def foo(): ... f"Not a docstring" ... >>> foo.__doc__ is None True
另请参阅
PEP 498
for the proposal that added formatted string literals, and
str.format()
, which uses a related format string mechanism.
There are three types of numeric literals: integers, floating point numbers, and imaginary numbers. There are no complex literals (complex numbers can be formed by adding a real number and an imaginary number).
Note that numeric literals do not include a sign; a phrase like
-1
is actually an expression composed of the unary operator ‘
-
’ and the literal
1
.
下列词法定义描述整数文字：
integer ::=decinteger|bininteger|octinteger|hexintegerdecinteger ::=nonzerodigit(["_"]digit)* | "0"+ (["_"] "0")* bininteger ::= "0" ("b" | "B") (["_"]bindigit)+ octinteger ::= "0" ("o" | "O") (["_"]octdigit)+ hexinteger ::= "0" ("x" | "X") (["_"]hexdigit)+ nonzerodigit ::= "1"..."9" digit ::= "0"..."9" bindigit ::= "0" | "1" octdigit ::= "0"..."7" hexdigit ::=digit| "a"..."f" | "A"..."F"
There is no limit for the length of integer literals apart from what can be stored in available memory.
Underscores are ignored for determining the numeric value of the literal. They can be used to group digits for enhanced readability. One underscore can occur between digits, and after base specifiers like
0x
.
Note that leading zeros in a non-zero decimal number are not allowed. This is for disambiguation with C-style octal literals, which Python used before version 3.0.
一些整数文字范例：
7 2147483647 0o177 0b100110111 3 79228162514264337593543950336 0o377 0xdeadbeef 100_000_000_000 0b_1110_0101
3.6 版改变： Underscores are now allowed for grouping purposes in literals.
浮点文字由以下词汇定义所描述：
floatnumber ::=pointfloat|exponentfloatpointfloat ::= [digitpart]fraction|digitpart"." exponentfloat ::= (digitpart|pointfloat)exponentdigitpart ::=digit(["_"]digit)* fraction ::= "."digitpartexponent ::= ("e" | "E") ["+" | "-"]digitpart
Note that the integer and exponent parts are always interpreted using radix 10. For example,
077e010
is legal, and denotes the same number as
77e10
. The allowed range of floating point literals is implementation-dependent. As in integer literals, underscores are supported for digit grouping.
一些浮点文字范例：
3.14 10. .001 1e100 3.14e-10 0e0 3.14_15_93
3.6 版改变： Underscores are now allowed for grouping purposes in literals.
虚数文字的描述是通过下列词法定义：
imagnumber ::= (floatnumber|digitpart) ("j" | "J")
An imaginary literal yields a complex number with a real part of 0.0. Complex numbers are represented as a pair of floating point numbers and have the same restrictions on their range. To create a complex number with a nonzero real part, add a floating point number to it, e.g.,
(3+4j)
。一些虚数文字范例：
3.14j 10.j 10j .001j 1e100j 3.14e-10j 3.14_15_93j
以下令牌是运算符：
+ - * ** / // % @ << >> & | ^ ~ := < > <= >= == !=
以下令牌充当语法中的分隔符：
( ) [ ] { }
, : . ; @ = ->
+= -= *= /= //= %= @=
&= |= ^= >>= <<= **=
The period can also occur in floating-point and imaginary literals. A sequence of three periods has a special meaning as an ellipsis literal. The second half of the list, the augmented assignment operators, serve lexically as delimiters, but also perform an operation.
The following printing ASCII characters have special meaning as part of other tokens or are otherwise significant to the lexical analyzer:
' " # \
The following printing ASCII characters are not used in Python. Their occurrence outside string literals and comments is an unconditional error:
$ ? `
脚注