string
— 常见字符串操作
¶
源代码： Lib/string.py
The
string
module contains a number of useful constants and classes, as well as some deprecated legacy functions that are also available as methods on strings. In addition, Python’s built-in string classes support the sequence type methods described in the
Sequence Types — str, unicode, list, tuple, bytearray, buffer, xrange
section, and also the string-specific methods described in the
字符串方法
section. To output formatted strings use template strings or the
%
operator described in the
字符串格式化操作
section. Also, see the
re
module for string functions based on regular expressions.
此模块中定义的常量：
string.
ascii_letters
¶
串联的
ascii_lowercase
and
ascii_uppercase
常量的描述见下文。此值不从属区域设置。
string.
ascii_lowercase
¶
小写字母
'abcdefghijklmnopqrstuvwxyz'
。此值不从属区域设置且不会改变。
string.
ascii_uppercase
¶
大写字母
'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
。此值不从属区域设置且不会改变。
string.
digits
¶
字符串
'0123456789'
.
string.
hexdigits
¶
字符串
'0123456789abcdefABCDEF'
.
string.
letters
¶
The concatenation of the strings
lowercase
and
uppercase
described below. The specific value is locale-dependent, and will be updated when
locale.setlocale()
被调用。
string.
lowercase
¶
A string containing all the characters that are considered lowercase letters. On most systems this is the string
'abcdefghijklmnopqrstuvwxyz'
. The specific value is locale-dependent, and will be updated when
locale.setlocale()
被调用。
string.
octdigits
¶
字符串
'01234567'
.
string.
punctuation
¶
被认为是标点符号的 ASCII 字符字符串，在
C
区域设置。
string.
printable
¶
String of characters which are considered printable. This is a combination of
digits
,
letters
,
punctuation
，和
whitespace
.
string.
uppercase
¶
A string containing all the characters that are considered uppercase letters. On most systems this is the string
'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
. The specific value is locale-dependent, and will be updated when
locale.setlocale()
被调用。
string.
whitespace
¶
A string containing all characters that are considered whitespace. On most systems this includes the characters space, tab, linefeed, return, formfeed, and vertical tab.
2.6 版新增。
The built-in str and unicode classes provide the ability to do complex variable substitutions and value formatting via the
str.format()
方法描述在
PEP 3101
。
Formatter
类在
string
module allows you to create and customize your own string formatting behaviors using the same implementation as the built-in
format()
方法。
format
(
format_string
,
*args
,
**kwargs
)
¶
The primary API method. It takes a format string and an arbitrary set of positional and keyword arguments. It is just a wrapper that calls
vformat()
.
vformat
(
format_string
,
args
,
kwargs
)
¶
This function does the actual work of formatting. It is exposed as a separate function for cases where you want to pass in a predefined dictionary of arguments, rather than unpacking and repacking the dictionary as individual arguments using the
*args
and
**kwargs
句法。
vformat()
does the work of breaking up the format string into character data and replacement fields. It calls the various methods described below.
此外，
Formatter
defines a number of methods that are intended to be replaced by subclasses:
parse
(
format_string
)
¶
Loop over the format_string and return an iterable of tuples (
literal_text
,
field_name
,
format_spec
,
conversion
). This is used by
vformat()
to break the string into either literal text, or replacement fields.
The values in the tuple conceptually represent a span of literal text followed by a single replacement field. If there is no literal text (which can happen if two replacement fields occur consecutively), then
literal_text
will be a zero-length string. If there is no replacement field, then the values of
field_name
,
format_spec
and
conversion
将是
None
.
get_field
(
field_name
,
args
,
kwargs
)
¶
Given
field_name
如返回通过
parse()
(see above), convert it to an object to be formatted. Returns a tuple (obj, used_key). The default version takes strings of the form defined in
PEP 3101
, such as “0[name]” or “label.title”.
args
and
kwargs
are as passed in to
vformat()
. The return value
used_key
has the same meaning as the
key
参数用于
get_value()
.
get_value
(
key
,
args
,
kwargs
)
¶
检索给定字段值。 key argument will be either an integer or a string. If it is an integer, it represents the index of the positional argument in args ; if it is a string, then it represents a named argument in kwargs .
The
args
parameter is set to the list of positional arguments to
vformat()
，和
kwargs
parameter is set to the dictionary of keyword arguments.
For compound field names, these functions are only called for the first component of the field name; Subsequent components are handled through normal attribute and indexing operations.
So for example, the field expression ‘0.name’ would cause
get_value()
to be called with a
key
argument of 0. The
name
attribute will be looked up after
get_value()
returns by calling the built-in
getattr()
函数。
If the index or keyword refers to an item that does not exist, then an
IndexError
or
KeyError
should be raised.
check_unused_args
(
used_args
,
args
,
kwargs
)
¶
Implement checking for unused arguments if desired. The arguments to this function is the set of all argument keys that were actually referred to in the format string (integers for positional arguments, and strings for named arguments), and a reference to the
args
and
kwargs
that was passed to vformat. The set of unused args can be calculated from these parameters.
check_unused_args()
is assumed to raise an exception if the check fails.
format_field
(
值
,
format_spec
)
¶
format_field()
只需调用全局
format()
内置。提供此方法以便子类可以覆盖它。
convert_field
(
值
,
conversion
)
¶
转换值 (返回通过
get_field()
) given a conversion type (as in the tuple returned by the
parse()
method). The default version understands ‘s’ (str), ‘r’ (repr) and ‘a’ (ascii) conversion types.
The
str.format()
方法和
Formatter
类共享相同格式字符串句法 (尽管在
Formatter
, subclasses can define their own format string syntax).
格式字符串包含 "置换字段" 环绕通过花括号
{}
. Anything that is not contained in braces is considered literal text, which is copied unchanged to the output. If you need to include a brace character in the literal text, it can be escaped by doubling:
{{
and
}}
.
置换字段的语法如下：
replacement_field ::= "{" [field_name] ["!" conversion] [":" format_spec] "}"
field_name ::= arg_name ("." attribute_name | "[" element_index "]")*
arg_name ::= [identifier | integer]
attribute_name ::= identifier
element_index ::= integer | index_string
index_string ::= <any source character except "]"> +
conversion ::= "r" | "s"
format_spec ::= <described in the next section>
In less formal terms, the replacement field can start with a
field_name
that specifies the object whose value is to be formatted and inserted into the output instead of the replacement field. The
field_name
is optionally followed by a
conversion
field, which is preceded by an exclamation point
'!'
，和
format_spec
, which is preceded by a colon
':'
. These specify a non-default format for the replacement value.
另请参阅 格式规范迷你语言 章节。
The
field_name
itself begins with an
arg_name
that is either a number or a keyword. If it’s a number, it refers to a positional argument, and if it’s a keyword, it refers to a named keyword argument. If the numerical arg_names in a format string are 0, 1, 2, … in sequence, they can all be omitted (not just some) and the numbers 0, 1, 2, … will be automatically inserted in that order. Because
arg_name
is not quote-delimited, it is not possible to specify arbitrary dictionary keys (e.g., the strings
'10'
or
':-]'
) within a format string. The
arg_name
can be followed by any number of index or attribute expressions. An expression of the form
'.name'
selects the named attribute using
getattr()
, while an expression of the form
'[index]'
does an index lookup using
__getitem__()
.
2.7 版改变：
可以省略位置自变量说明符对于
str.format()
and
unicode.format()
，所以
'{} {}'
相当于
'{0} {1}'
,
u'{} {}'
相当于
u'{0} {1}'
.
一些简单格式字符串范例：
"First, thou shalt count to {0}" # References first positional argument "Bring me a {}" # Implicitly references the first positional argument "From {} to {}" # Same as "From {0} to {1}" "My quest is {name}" # References keyword argument 'name' "Weight in tons {0.weight}" # 'weight' attribute of first positional arg "Units destroyed: {players[0]}" # First element of keyword argument 'players'.
The
conversion
field causes a type coercion before formatting. Normally, the job of formatting a value is done by the
__format__()
method of the value itself. However, in some cases it is desirable to force a type to be formatted as a string, overriding its own definition of formatting. By converting the value to a string before calling
__format__()
, the normal formatting logic is bypassed.
Two conversion flags are currently supported:
'!s'
调用
str()
on the value, and
'!r'
调用
repr()
.
一些范例：
"Harold's a clever {0!s}" # Calls str() on the argument first "Bring out the holy {name!r}" # Calls repr() on the argument first
The format_spec field contains a specification of how the value should be presented, including such details as field width, alignment, padding, decimal precision and so on. Each value type can define its own “formatting mini-language” or interpretation of the format_spec .
Most built-in types support a common formatting mini-language, which is described in the next section.
A format_spec field can also include nested replacement fields within it. These nested replacement fields may contain a field name, conversion flag and format specification, but deeper nesting is not allowed. The replacement fields within the format_spec are substituted before the format_spec string is interpreted. This allows the formatting of a value to be dynamically specified.
见 格式范例 章节举的一些范例。
“Format specifications” are used within replacement fields contained within a format string to define how individual values are presented (see
格式字符串语法
). They can also be passed directly to the built-in
format()
function. Each formattable type may define how the format specification is to be interpreted.
大多数内置类型为格式规范实现了下列选项，尽管某些格式选项只支持数值类型。
A general convention is that an empty format string (
""
) produces the same result as if you had called
str()
on the value. A non-empty format string typically modifies the result.
一般形式的 标准格式说明符 is:
format_spec ::= [[fill]align][sign][#][0][width][,][.precision][type] fill ::= <any character> align ::= "<" | ">" | "=" | "^" sign ::= "+" | "-" | " " width ::=integerprecision ::=integertype ::= "b" | "c" | "d" | "e" | "E" | "f" | "F" | "g" | "G" | "n" | "o" | "s" | "x" | "X" | "%"
若有效
align
值被指定，它的前面可以加
fill
character that can be any character and defaults to a space if omitted. It is not possible to use a literal curly brace (“
{
或
}
) 作为
fill
character when using the
str.format()
method. However, it is possible to insert a curly brace with a nested replacement field. This limitation doesn’t affect the
format()
函数。
各对齐选项的含义如下：
|
选项 |
含义 |
|---|---|
|
|
强制字段在可用空间内左对齐 (这是大多数对象的默认值)。 |
|
|
Forces the field to be right-aligned within the available space (this is the default for numbers). |
|
|
Forces the padding to be placed after the sign (if any) but before the digits. This is used for printing fields in the form ‘+000000120’. This alignment option is only valid for numeric types. It becomes the default when ‘0’ immediately precedes the field width. |
|
|
强制字段在可用空间内居中。 |
Note that unless a minimum field width is defined, the field width will always be the same size as the data to fill it, so that the alignment option has no meaning in this case.
The sign option is only valid for number types, and can be one of the following:
|
选项 |
含义 |
|---|---|
|
|
indicates that a sign should be used for both positive as well as negative numbers. |
|
|
indicates that a sign should be used only for negative numbers (this is the default behavior). |
| space | indicates that a leading space should be used on positive numbers, and a minus sign on negative numbers. |
The
'#'
option is only valid for integers, and only for binary, octal, or hexadecimal output. If present, it specifies that the output will be prefixed by
'0b'
,
'0o'
，或
'0x'
，分别。
The
','
选项表示使用逗号作为千位分隔符。对于区域设置感知分隔符，使用
'n'
整数表示类型代替。
2.7 版改变：
添加
','
选项 (另请参阅
PEP 378
).
width is a decimal integer defining the minimum field width. If not specified, then the field width will be determined by the content.
When no explicit alignment is given, preceding the
width
field by a zero (
'0'
) character enables sign-aware zero-padding for numeric types. This is equivalent to a
fill
character of
'0'
with an
alignment
type of
'='
.
The
precision
is a decimal number indicating how many digits should be displayed after the decimal point for a floating point value formatted with
'f'
and
'F'
, or before and after the decimal point for a floating point value formatted with
'g'
or
'G'
. For non-number types the field indicates the maximum field size - in other words, how many characters will be used from the field content. The
precision
is not allowed for integer values.
最后， type 确定应如何呈现数据。
可用的字符串表示类型：
|
类型 |
含义 |
|---|---|
|
|
字符串格式。这是用于字符串的默认类型，且可以省略。 |
| None |
如同
|
可用的整数表示类型：
|
类型 |
含义 |
|---|---|
|
|
Binary format. Outputs the number in base 2. |
|
|
Character. Converts the integer to the corresponding unicode character before printing. |
|
|
Decimal Integer. Outputs the number in base 10. |
|
|
Octal format. Outputs the number in base 8. |
|
|
Hex format. Outputs the number in base 16, using lower- case letters for the digits above 9. |
|
|
Hex format. Outputs the number in base 16, using upper- case letters for the digits above 9. |
|
|
数字。这如同
|
| None |
如同
|
In addition to the above presentation types, integers can be formatted with the floating point presentation types listed below (except
'n'
and
None
). When doing so,
float()
is used to convert the integer to a floating point number before formatting.
The available presentation types for floating point and decimal values are:
|
类型 |
含义 |
|---|---|
|
|
Exponent notation. Prints the number in scientific notation using the letter ‘e’ to indicate the exponent. The default precision is
|
|
|
Exponent notation. Same as
|
|
|
Fixed-point notation. Displays the number as a fixed-point number. The default precision is
|
|
|
Fixed point notation. Same as
|
|
|
General format. For a given precision
The precise rules are as follows: suppose that the result formatted with presentation type
Positive and negative infinity, positive and negative zero, and nans, are formatted as
A precision of
|
|
|
General format. Same as
|
|
|
数字。这如同
|
|
|
Percentage. Multiplies the number by 100 and displays in fixed (
|
| None |
如同
|
This section contains examples of the
str.format()
syntax and comparison with the old
%
格式化。
In most of the cases the syntax is similar to the old
%
-formatting, with the addition of the
{}
和采用
:
used instead of
%
。例如，
'%03.2f'
可被翻译成
'{:03.2f}'
.
The new format syntax also supports new and different options, shown in the following examples.
按位置访问自变量：
>>> '{0}, {1}, {2}'.format('a', 'b', 'c') 'a, b, c' >>> '{}, {}, {}'.format('a', 'b', 'c') # 2.7+ only 'a, b, c' >>> '{2}, {1}, {0}'.format('a', 'b', 'c') 'c, b, a' >>> '{2}, {1}, {0}'.format(*'abc') # unpacking argument sequence 'c, b, a' >>> '{0}{1}{0}'.format('abra', 'cad') # arguments' indices can be repeated 'abracadabra'
按名称访问自变量：
>>> 'Coordinates: {latitude}, {longitude}'.format(latitude='37.24N', longitude='-115.81W') 'Coordinates: 37.24N, -115.81W' >>> coord = {'latitude': '37.24N', 'longitude': '-115.81W'} >>> 'Coordinates: {latitude}, {longitude}'.format(**coord) 'Coordinates: 37.24N, -115.81W'
访问自变量的属性：
>>> c = 3-5j >>> ('The complex number {0} is formed from the real part {0.real} ' ... 'and the imaginary part {0.imag}.').format(c) 'The complex number (3-5j) is formed from the real part 3.0 and the imaginary part -5.0.' >>> class Point(object): ... def __init__(self, x, y): ... self.x, self.y = x, y ... def __str__(self): ... return 'Point({self.x}, {self.y})'.format(self=self) ... >>> str(Point(4, 2)) 'Point(4, 2)'
访问自变量的项：
>>> coord = (3, 5) >>> 'X: {0[0]}; Y: {0[1]}'.format(coord) 'X: 3; Y: 5'
替换
%s
and
%r
:
>>> "repr() shows quotes: {!r}; str() doesn't: {!s}".format('test1', 'test2') "repr() shows quotes: 'test1'; str() doesn't: test2"
对齐文本并指定宽度：
>>> '{:<30}'.format('left aligned') 'left aligned ' >>> '{:>30}'.format('right aligned') ' right aligned' >>> '{:^30}'.format('centered') ' centered ' >>> '{:*^30}'.format('centered') # use '*' as a fill char '***********centered***********'
替换
%+f
,
%-f
，和
% f
并指定正负号：
>>> '{:+f}; {:+f}'.format(3.14, -3.14) # show it always '+3.140000; -3.140000' >>> '{: f}; {: f}'.format(3.14, -3.14) # show a space for positive numbers ' 3.140000; -3.140000' >>> '{:-f}; {:-f}'.format(3.14, -3.14) # show only the minus -- same as '{:f}; {:f}' '3.140000; -3.140000'
替换
%x
and
%o
并把值转换成不同的基数：
>>> # format also supports binary numbers >>> "int: {0:d}; hex: {0:x}; oct: {0:o}; bin: {0:b}".format(42) 'int: 42; hex: 2a; oct: 52; bin: 101010' >>> # with 0x, 0o, or 0b as prefix: >>> "int: {0:d}; hex: {0:#x}; oct: {0:#o}; bin: {0:#b}".format(42) 'int: 42; hex: 0x2a; oct: 0o52; bin: 0b101010'
使用逗号作为千位分隔符：
>>> '{:,}'.format(1234567890) '1,234,567,890'
表达百分比：
>>> points = 19.5 >>> total = 22 >>> 'Correct answers: {:.2%}'.format(points/total) 'Correct answers: 88.64%'
使用特定类型格式：
>>> import datetime >>> d = datetime.datetime(2010, 7, 4, 12, 15, 58) >>> '{:%Y-%m-%d %H:%M:%S}'.format(d) '2010-07-04 12:15:58'
嵌套自变量和更复杂范例：
>>> for align, text in zip('<^>', ['left', 'center', 'right']): ... '{0:{fill}{align}16}'.format(text, fill=align, align=align) ... 'left<<<<<<<<<<<<' '^^^^^center^^^^^' '>>>>>>>>>>>right' >>> >>> octets = [192, 168, 0, 1] >>> '{:02X}{:02X}{:02X}{:02X}'.format(*octets) 'C0A80001' >>> int(_, 16) 3232235521 >>> >>> width = 5 >>> for num in range(5,12): ... for base in 'dXob': ... print '{0:{width}{base}}'.format(num, base=base, width=width), ... print ... 5 5 5 101 6 6 6 110 7 7 7 111 8 8 10 1000 9 9 11 1001 10 A 12 1010 11 B 13 1011
2.4 版新增。
Templates provide simpler string substitutions as described in
PEP 292
. Instead of the normal
%
-based substitutions, Templates support
$
-based substitutions, using the following rules:
$$
是转义；它被替换采用单个
$
.
$identifier
names a substitution placeholder matching a mapping key of
"identifier"
。默认情况下，
"identifier"
must spell a Python identifier. The first non-identifier character after the
$
character terminates this placeholder specification.
${identifier}
相当于
$identifier
. It is required when valid identifier characters follow the placeholder but are not part of the placeholder, such as
"${noun}ification"
.
任何其它外观的
$
in the string will result in a
ValueError
being raised.
The
string
模块提供
Template
class that implements these rules. The methods of
Template
是：
string.
Template
(
template
)
¶
构造函数接受单模板字符串自变量。
substitute
(
映射
[
,
**kws
]
)
¶
Performs the template substitution, returning a new string. 映射 is any dictionary-like object with keys that match the placeholders in the template. Alternatively, you can provide keyword arguments, where the keywords are the placeholders. When both 映射 and kws are given and there are duplicates, the placeholders from kws take precedence.
safe_substitute
(
映射
[
,
**kws
]
)
¶
像
substitute()
, except that if placeholders are missing from
映射
and
kws
, instead of raising a
KeyError
exception, the original placeholder will appear in the resulting string intact. Also, unlike with
substitute()
, any other appearances of the
$
will simply return
$
而不是引发
ValueError
.
While other exceptions may still occur, this method is called “safe” because it always tries to return a usable string instead of raising an exception. In another sense,
safe_substitute()
may be anything other than safe, since it will silently ignore malformed templates containing dangling delimiters, unmatched braces, or placeholders that are not valid Python identifiers.
Template
实例还提供一公共数据属性：
template
¶
This is the object passed to the constructor’s template argument. In general, you shouldn’t change it, but read-only access is not enforced.
这里是如何使用 Template 的范例：
>>> from string import Template >>> s = Template('$who likes $what') >>> s.substitute(who='tim', what='kung pao') 'tim likes kung pao' >>> d = dict(who='tim') >>> Template('Give $who $100').substitute(d) Traceback (most recent call last): ... ValueError: Invalid placeholder in string: line 1, col 11 >>> Template('$who likes $what').substitute(d) Traceback (most recent call last): ... KeyError: 'what' >>> Template('$who likes $what').safe_substitute(d) 'tim likes $what'
Advanced usage: you can derive subclasses of
Template
to customize the placeholder syntax, delimiter character, or the entire regular expression used to parse template strings. To do this, you can override these class attributes:
delimiter
– This is the literal string describing a placeholder introducing delimiter. The default value is
$
. Note that this should
not
be a regular expression, as the implementation will call
re.escape()
on this string as needed.
idpattern
– This is the regular expression describing the pattern for non-braced placeholders (the braces will be added automatically as appropriate). The default value is the regular expression
[_a-z][_a-z0-9]*
.
Alternatively, you can provide the entire regular expression pattern by overriding the class attribute pattern . If you do this, the value must be a regular expression object with four named capturing groups. The capturing groups correspond to the rules given above, along with the invalid placeholder rule:
escaped
– This group matches the escape sequence, e.g.
$$
, in the default pattern.
命名 – This group matches the unbraced placeholder name; it should not include the delimiter in capturing group.
braced – This group matches the brace enclosed placeholder name; it should not include either the delimiter or braces in the capturing group.
invalid – This group matches any other delimiter pattern (usually a single delimiter), and it should appear last in the regular expression.
The following functions are available to operate on string and Unicode objects. They are not available as string methods.
string.
capwords
(
s
[
,
sep
]
)
¶
把自变量拆分成单词，使用
str.split()
，大写每单词使用
str.capitalize()
, and join the capitalized words using
str.join()
. If the optional second argument
sep
is absent or
None
, runs of whitespace characters are replaced by a single space and leading and trailing whitespace are removed, otherwise
sep
is used to split and join the words.
string.
maketrans
(
from
,
to
)
¶
Return a translation table suitable for passing to
translate()
, that will map each character in
from
into the character at the same position in
to
;
from
and
to
must have the same length.
注意
Don’t use strings derived from
lowercase
and
uppercase
as arguments; in some locales, these don’t have the same length. For case conversions, always use
str.lower()
and
str.upper()
.
The following list of functions are also defined as methods of string and Unicode objects; see section 字符串方法 for more information on those. You should consider these functions as deprecated, although they will not be removed until Python 3. The functions defined in this module are:
string.
atof
(
s
)
¶
Deprecated since version 2.0:
使用
float()
内置函数。
Convert a string to a floating point number. The string must have the standard syntax for a floating point literal in Python, optionally preceded by a sign (
+
or
-
). Note that this behaves identical to the built-in function
float()
when passed a string.
注意
When passing in a string, values for NaN and Infinity may be returned, depending on the underlying C library. The specific set of strings accepted which cause these values to be returned depends entirely on the C library and is known to vary.
string.
atoi
(
s
[
,
base
]
)
¶
Deprecated since version 2.0:
使用
int()
内置函数。
Convert string
s
to an integer in the given
base
. The string must consist of one or more digits, optionally preceded by a sign (
+
or
-
)。
base
defaults to 10. If it is 0, a default base is chosen depending on the leading characters of the string (after stripping the sign):
0x
or
0X
means 16,
0
means 8, anything else means 10. If
base
is 16, a leading
0x
or
0X
is always accepted, though not required. This behaves identically to the built-in function
int()
when passed a string. (Also note: for a more flexible interpretation of numeric literals, use the built-in function
eval()
)。
string.
atol
(
s
[
,
base
]
)
¶
Deprecated since version 2.0:
使用
long()
内置函数。
Convert string
s
to a long integer in the given
base
. The string must consist of one or more digits, optionally preceded by a sign (
+
or
-
)。
base
自变量有相同含义如
atoi()
. A trailing
l
or
L
is not allowed, except if the base is 0. Note that when invoked without
base
or with
base
set to 10, this behaves identical to the built-in function
long()
when passed a string.
string.
capitalize
(
word
)
¶
Return a copy of word with only its first character capitalized.
string.
expandtabs
(
s
[
,
tabsize
]
)
¶
Expand tabs in a string replacing them by one or more spaces, depending on the current column and the given tab size. The column number is reset to zero after each newline occurring in the string. This doesn’t understand other non-printing characters or escape sequences. The tab size defaults to 8.
string.
find
(
s
,
sub
[
,
start
[
,
end
]
]
)
¶
Return the lowest index in
s
where the substring
sub
is found such that
sub
is wholly contained in
s[start:end]
。返回
-1
on failure. Defaults for
start
and
end
and interpretation of negative values is the same as for slices.
string.
index
(
s
,
sub
[
,
start
[
,
end
]
]
)
¶
像
find()
but raise
ValueError
当找不到子字符串时。
string.
rindex
(
s
,
sub
[
,
start
[
,
end
]
]
)
¶
像
rfind()
but raise
ValueError
当找不到子字符串时。
string.
count
(
s
,
sub
[
,
start
[
,
end
]
]
)
¶
Return the number of (non-overlapping) occurrences of substring
sub
在字符串
s[start:end]
. Defaults for
start
and
end
and interpretation of negative values are the same as for slices.
string.
lower
(
s
)
¶
Return a copy of s , but with upper case letters converted to lower case.
string.
split
(
s
[
,
sep
[
,
maxsplit
]
]
)
¶
Return a list of the words of the string
s
. If the optional second argument
sep
is absent or
None
, the words are separated by arbitrary strings of whitespace characters (space, tab, newline, return, formfeed). If the second argument
sep
is present and not
None
, it specifies a string to be used as the word separator. The returned list will then have one more item than the number of non-overlapping occurrences of the separator in the string. If
maxsplit
is given, at most
maxsplit
number of splits occur, and the remainder of the string is returned as the final element of the list (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).
The behavior of split on an empty string depends on the value of
sep
。若
sep
is not specified, or specified as
None
, the result will be an empty list. If
sep
is specified as any string, the result will be a list containing one element which is an empty string.
string.
rsplit
(
s
[
,
sep
[
,
maxsplit
]
]
)
¶
Return a list of the words of the string
s
, scanning
s
from the end. To all intents and purposes, the resulting list of words is the same as returned by
split()
, except when the optional third argument
maxsplit
is explicitly specified and nonzero. If
maxsplit
is given, at most
maxsplit
number of splits – the
rightmost
ones – occur, and the remainder of the string is returned as the first element of the list (thus, the list will have at most
maxsplit+1
elements).
2.4 版新增。
string.
splitfields
(
s
[
,
sep
[
,
maxsplit
]
]
)
¶
This function behaves identically to
split()
. (In the past,
split()
was only used with one argument, while
splitfields()
was only used with two arguments.)
string.
join
(
words
[
,
sep
]
)
¶
Concatenate a list or tuple of words with intervening occurrences of
sep
。默认值对于
sep
is a single space character. It is always true that
string.join(string.split(s, sep), sep)
等于
s
.
string.
joinfields
(
words
[
,
sep
]
)
¶
This function behaves identically to
join()
. (In the past,
join()
was only used with one argument, while
joinfields()
was only used with two arguments.) Note that there is no
joinfields()
method on string objects; use the
join()
method instead.
string.
lstrip
(
s
[
,
chars
]
)
¶
Return a copy of the string with leading characters removed. If
chars
被省略或
None
, whitespace characters are removed. If given and not
None
,
chars
must be a string; the characters in the string will be stripped from the beginning of the string this method is called on.
Changed in version 2.2.3: The chars 参数被添加。 chars parameter cannot be passed in earlier 2.2 versions.
string.
rstrip
(
s
[
,
chars
]
)
¶
Return a copy of the string with trailing characters removed. If
chars
被省略或
None
, whitespace characters are removed. If given and not
None
,
chars
must be a string; the characters in the string will be stripped from the end of the string this method is called on.
Changed in version 2.2.3: The chars 参数被添加。 chars parameter cannot be passed in earlier 2.2 versions.
string.
strip
(
s
[
,
chars
]
)
¶
Return a copy of the string with leading and trailing characters removed. If
chars
被省略或
None
, whitespace characters are removed. If given and not
None
,
chars
must be a string; the characters in the string will be stripped from the both ends of the string this method is called on.
Changed in version 2.2.3: The chars 参数被添加。 chars parameter cannot be passed in earlier 2.2 versions.
string.
swapcase
(
s
)
¶
Return a copy of s , but with lower case letters converted to upper case and vice versa.
string.
translate
(
s
,
table
[
,
deletechars
]
)
¶
Delete all characters from
s
that are in
deletechars
(if present), and then translate the characters using
table
, which must be a 256-character string giving the translation for each character value, indexed by its ordinal. If
table
is
None
, then only the character deletion step is performed.
string.
upper
(
s
)
¶
Return a copy of s , but with lower case letters converted to upper case.
string.
ljust
(
s
,
width
[
,
fillchar
]
)
¶
string.
rjust
(
s
,
width
[
,
fillchar
]
)
¶
string.
center
(
s
,
width
[
,
fillchar
]
)
¶
These functions respectively left-justify, right-justify and center a string in a field of given width. They return a string that is at least width characters wide, created by padding the string s with the character fillchar (default is a space) until the given width on the right, left or both sides. The string is never truncated.
string.
zfill
(
s
,
width
)
¶
Pad a numeric string s on the left with zero digits until the given width is reached. Strings starting with a sign are handled correctly.
string.
replace
(
s
,
old
,
new
[
,
maxreplace
]
)
¶
Return a copy of string s with all occurrences of substring old 被替换通过 new 。若可选自变量 maxreplace is given, the first maxreplace 出现被替换。