Python string

Learn how to use strings in Python as follows.

print(dir(str))

['__add__', '__class__', '__contains__', '__delattr__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__ ', '__getitem__', '__getnewargs__', '__gt__', '__hash__', '__init__', '__iter__', '__le__', '__len__', '__lt__', '__mod__', '__mul__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__rmod__', '__rmul__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', 'capitalize', 'casefold', 'center ', 'count', 'encode', 'endswith', 'expandtabs', 'find', 'format', 'format_map', 'index', 'isalnum', 'isalpha', 'isdecimal', 'isdigit', 'isidentifier', 'islower', 'isnumeric', 'isprintable', 'isspace', 'istitle', 'isupper', 'join', 'ljust', 'lower', 'lstrip', 'maketrans', 'partition ', 'replace', 'rfind', 'rindex', 'rjust', 'rpartition', 'rsplit', 'rstrip', 'split', 'splitlines', 'startswith', 'strip', 'swapcase', 'title', 'translate', 'upper', 'zfill']

The above are all the methods of strings, look at them one by one, a total of 44

1. Return the first letter capitalized

capitalize(...)

capitalize() -> string

>>>a = 'hello world'
>>> b = a.capitalize()
>>> print (b)
Hello world

2． Fill specific characters to the specified length

center(...)

S.center(width[, fillchar]) -> string

>>> a = 'linux'
>>> print a.center(7,'h')
hlinuxh
>>> print a.center(8,'h')
hlinuxhh
>>> print a.center(9,'h')
hhlinuxhh

3. Find the number of times a string appears

count(...)

S.count(sub[, start[, end]]) -> int

>>> a = "this is my dog, i love this dog and it's a good dog!"
>>> print a.count('dog')
3
>>> print a.count('dog',15)
2
>>> print a.count('dog',15,30)
0
>>> print a.count('dog',15,32)
1

4. Decode the string in the specified encoding format. The default encoding is string encoding (suitable for processing Chinese in python2) decode(...)

S.decode([encoding[,errors]]) ->object

b = 'strid'
>>> b.decode('utf-8')
u'strid'

5. Used to determine whether the string is Specifies the end of the suffix, returns True if it ends with the specified suffix, otherwise returns False. The optional parameters "start" and "end" are the start and end positions of the retrieved string

Endswith(...)

S.endswith(suffix[,start[, end]]) ->bool

>>> shaw = 'I am shaw,what\'s your name ?'
>>> shaw.endswith('?')
True
>>> shaw.endswith('w',7,9)
True
>>> shaw.endswith('w',7,8)
False

6 .Convert the tab symbol ('t') in the string to spaces. The default number of spaces for the tab symbol ('t') is 8. tabsize -- specifies the conversion of the tab symbol ('t') in the string to spaces. number of characters.

​ expandtabs(...)

​ S.expandtabs([tabsize])-> string

>>> info = 'today is a good d\tay'
>>> print info.expandtabs()
today is a good d       ay
>>> print info.expandtabs(4)   # 把tab装换成4个空格
today is a good d   ay         
>>> printinfo.expandtabs(1)
today is a good d ay          # 把tab装换成1个空格

7. Detect whether the string contains the substring str. If you specify the beg (start) and end (end) range, Then check whether it is contained in the specified range. If it contains a substring, return the starting index value, otherwise return -1.

find(...)

S.find(sub [,start [,end]])-> int

>>> a = 'stivenwang'
>>> a.find('w')
6
>>> a.find('w',9)
-1
>>> a.find('w',9,11)
-1

8. Format string output (method is similar to %, but the order can be specified)

format(...)

S.format(*args, **kwargs)-> string

>>> name = 'StivenWang'
>>> fruit = 'apple'
>>> print 'my name is {},I like {}'.format(name,fruit)
my name is StivenWang,I like apple
>>> print 'my name is {1},I like {0}'.format(fruit,name)
my name is StivenWang,I like apple
>>> print 'my name is {mingzi},I like{shuiguo}'.format(shuiguo=fruit,mingzi=name)
my name is StivenWang,I like apple

9. Detect string in string Whether the substring str is included. If it exists, return the index value of str in the string. If you specify the beg (start) and end (end) range, check whether it is included in the specified range. This method is the same as the python find() method. The same, except that if str is not in string, an exception will be reported (ValueError: substring not found).

index(...)

S.index(sub [,start [,end]])-> int

>>> str1 = "this is string example....wow!!!"
>>> str2 = "exam"
>>> print str1.index(str2)
15
>>> print str1.index(str2,20)
Traceback (most recent call last):
  File "<input>",line 1, in <module>
ValueError: substringnot found报错

10. Detect whether the string consists of letters or numbers.

 isalnum(...)

 S.isalnum() -> bool

>>> a = '123'
>>> a.isalnum()
True
>>> b = 'shaw'
>>> b.isalnum()
True
>>> c = 'shaw123'
>>> c.isalnum()
True
>>> d = 'th 123'
>>> d.isalnum()
False

11. Check whether the string consists of letters only

 isalpha(...)

 S.isalpha() -> bool

>> a = '123'
>>> a.isalpha()
False
>>> b = '123shaw'
>>> b.isalpha()
False
>>> c = 'shaw'
>>> c.isalpha()
True
>>> d = 'sha w'
>>> d.isalpha()
False

12. Check whether a string consists only of numbers.

 isdigit(...)

 S.isdigit() -> bool

>>> a = '123'
>>> a.isdigit()
True
>>> b = 'shaw'
>>> b.isdigit()
False
>>> c = '123shaw'
>>> c.isdigit()
False

13. Check whether the string consists of lowercase letters.

 islower(...)

 S.islower() -> bool

>>> a = 'shaw'
>>> a.islower()
True
>>> b = '123'
>>> a.islower()
True
>>> c = '123shaw'
>>> c.islower()
True
>>> d = 'SHAW'
>>> d.islower()
False
>>> e = '123SHAW'
>>> e.islower()
False

14. Check whether the string consists only of spaces.

isspace(...)

    S.isspace() -> bool

>>> a = ' '
>>> a.isspace()
True
>>> a = '123'
>>> a.isspace()
False
>>> a = 'shaw'
>>> a.isspace()
False

15.检测字符串中所有的单词拼写首字母是否为大写，且其他字母为小写。

    istitle(...) 

    S.istitle() -> bool

>>> a = 'Shaw'
>>> a.istitle()
True
>>> a = 'Shaw123'
>>> a.istitle()
True
>>> a = '123'
>>> a.istitle()
False

16.检测字符串中所有的字母是否都为大写

    isupper(...)

      S.isupper() -> bool

>>> a = '123'
>>> a.isupper()
False
>>> a = 'Shaw'
>>> a.isupper()
False
>>> a = 'Shaw123'
>>> a.isupper()
False
>>> a = 'SHAW123'
>>> a.isupper()
True

17.用于将序列中的元素以指定的字符连接生成一个新的字符串。

join(...)

    S.join(iterable) ->string

>>> a = '-'
>>> b = 'shaw'
>>> print a.join(b)
s-h-a-w

18.返回一个原字符串左对齐,并使用空格填充至指定长度的新字符串。如果指定的长度小于原字符串的长度则返回原字符串。

    ljust(...)

    S.ljust(width[, fillchar])-> string

    width -- 指定字符串长度

    fillchar -- 填充字符，默认为空格

>>> s = 'shaw'
>>> s.ljust(10)
'shaw      '
>>> s.ljust(10,'8')
'shaw888888'

19.转换字符串中所有大写字符为小写。

    Lower(...)

    S.lower() -> string

>>> s = 'PYTHON'
>>> s.lower()
'python'
>>> s = 'PYTHON123'
>>> s.lower()
'python123'

20.用于截掉字符串左边的空格或指定字符。

    lstrip(...)

    S.lstrip([chars]) ->string or unicode

>>> s = '%%%shaw'
>>> s.lstrip('%')
'shaw'
>>> s = '   shaw'
>>> s.lstrip()
'shaw

123456    >>> s = '%%%shaw'>>> s.lstrip('%')'shaw'>>> s = '   shaw'>>> s.lstrip()'shaw'    

21.根据指定的分隔符将字符串进行分割（返回一个3元的元组，第一个为分隔符左边的子串，第二个为分隔符本身，第三个为分隔符右边的子串）

    partition(...)

    S.partition(sep) ->(head, sep, tail)

>>> S = 'are you know:lilin is lowser'
>>> S.partition('lilin')
('are you know:', 'lilin', ' is lowser')

22.把字符串中的 old（旧字符串）替换成 new(新字符串)，如果指定第三个参数max，则替换不超过 max 次。

    replace(...)

    S.replace(old, new[,count]) -> string

>>> S = 'shaw'
>>> S.replace('sh','LI')
'LIaw'

23.返回字符串最后一次出现的位置，如果没有匹配项则返回-1。

    rfind(...)

    S.rfind(sub [,start[,end]]) -> int

    str -- 查找的字符串

    beg -- 开始查找的位置，默认为0

    end -- 结束查找位置，默认为字符串的长度。

>>> s = 'lilin is good li lao ban'
>>> s.rfind('li')
14
>>> s.rfind('li',0,8)
2

24.返回子字符串 str 在字符串中最后出现的位置，如果没有匹配的字符串会报异常，你可以指定可选参数[beg:end]设置查找的区间。

    rindex(...)

    S.rindex(sub [,start[,end]]) -> int

    语法：

      str.rindex(str,beg=0 end=len(string))

>>> s = 'my name is shaw'
>>> s.rindex('s')
11
>>> s.rindex('s',5,10)
9
>>> s.rindex('s',2,8)
Traceback (most recent call last):
  File "<input>",line 1, in <module>
ValueError: substring not found

25.返回的原/新字符串右对齐，且默认使用空格填充至指定长度（width）的新字符串。如果指定的长度（width）小于原字符串的长度则返回原字符串

    rjust(...)

    S.rjust(width[, fillchar])-> string

    语法：

      str.rjust(width[,fillchar])

       width -- 指定填充指定字符后新字符串的总长度.

       fillchar– 要填充的字符，默认为空格。

>>> s = 'sch'
>>> s.rjust(20)
'                 sch'
>>> s.rjust(20,'0')
'00000000000000000sch'
>>> s.rjust(20,'H')
'HHHHHHHHHHHHHHHHHsch'

26.删除 string 字符串末尾的指定字符（默认为空格）.

    rstrip(...)

    S.rstrip([chars]) ->string or unicode

    语法：

      str.rstrip([chars])

>>> s = 'shaw\n'
>>> s.rstrip('\n')
'shaw'

27.通过指定分隔符对字符串进行切片，如果参数num有指定值，则仅分隔 num 个子字符串

    split(...)

    S.split([sep [,maxsplit]])-> list ofstrings

    语法：

   str.split(str="",num=string.count(str)).

>>> s = 'shaw\nlinux\nmac'
>>> s.split('\n')
['shaw', 'linux', 'mac']
>>> s.split('\n',1)
['shaw', 'linux\nmac']

28.按照行分隔，返回一个包含各行作为元素的列表，如果 num 指定则仅切片 num 个行.

    splitlines(...)

    S.splitlines(keepends=False)-> list ofstrings

    语法：

      str.splitlines( num=string.count('\n'))

       num -- 分割行的次数。

>>> s = 'what\'s your name?\n my name is shaw\n how old areyou?'
>>> s.splitlines()
["what's your name?", ' my name is shaw', ' how old areyou?']
>>> s.splitlines(1)
["what's your name?\n", ' my name is shaw\n', ' how old areyou?']
>>> s.splitlines(3)

29.用于检查字符串是否是以指定子字符串开头，如果是则返回 True，否则返回 False。如果参数 beg 和 end指定值，则在指定范围内检查。

    startswith(...)

    S.startswith(prefix[,start[, end]]) ->bool

    语法：

    str.startswith(str,beg=0,end=len(string))

    str -- 检测的字符串。

    strbeg -- 可选参数用于设置字符串检测的起始位置。

    strend -- 可选参数用于设置字符串检测的结束位置。

>>> s = 'my name is shaw'
>>> s.startswith('my')
True
>>> s.startswith('my',10,15)
False

30.用于移除字符串头尾指定的字符（默认为空格）。

    strip(...)

    S.strip([chars]) ->string or unicode

>>> s = 'my name is sam'
>>> s.strip('m')
'y name is sa'

31.用于对字符串的大小写字母进行转换(小写转大写，大写转小写)

    swapcase(...)

    S.swapcase() -> string

>>> s = 'stiven'
>>> s.swapcase()
'STIVEN'
>>> s = 'SHAW'
>>> s.swapcase()
'shaw'

32.返回"标题化"的字符串,就是说所有单词都是以大写开始，其余字母均为小写。

    title(...)

    S.title() -> string

>>> s = 'my name is shaw'
>>> s.title()
'My Name Is Shaw'

33.根据参数table给出的表(包含 256 个字符)转换字符串的字符, 并返回翻译后的字符串。要过滤掉的字符放到del 参数中

    translate(...)

    S.translate(table [,deletechars])->string

    语法：

      str.translate(table[, deletechars])

       table -- 翻译表，翻译表是通过maketrans方法转换而来。

      deletechars -- 字符串中要过滤的字符列表。

>>> from string import maketrans
suchas = maketrans('sm','@$')
>>> s = 'this is sam\'s dog'
>>> s
"this is sam's dog"
>>> s.translate(suchas)
"thi@ i@ @a$'@ dog"
>>> s.translate(suchas,'dog') 去除d,o,g字符
"thi@ i@ @a$'@ "

34.将字符串中的小写字母转为大写字母

    upper(...)

    S.upper() -> string

>>> s = 'sam'
>>> s.upper()
'SAM'
>>> s = '23sam'
>>> s.upper()
'23SAM'
>>> s = '23s am'
>>> s.upper()
'23S AM'

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