1、count(self, sub, start=None, end=None): # real signature unknown; restored from __doc__
---取字符串当中 字符出现的次数，start,end 默认为空 表示字符从头到尾。 start是从第几个字符开始，第一字符位是0.
S.count(sub[, start[, end]]) -> int
例如：
i1 = "xuexipython"
print (i1.count('x'))
----“xuexipython” 当中 字符‘x’ 出现的次数 为2次。
print (i1.count('x',1,20))
----“xuexipython” 当中 从u字符开始，字符‘x’ 出现的次数 为1次。
2、capitalize(self): # real signature unknown; restored from __doc__
"""
S.capitalize() -> string
---字符串首字母转换为大写
Return a copy of the string S with only its first character
capitalized.
例如：
i1 = "xuexipython"
print (i1.capitalize())
---结果为：“Xuexipython”
3、center(self, width, fillchar=None): # real signature unknown; restored from __doc__
"""指定字符串长度 然后字符居中 默认用空格填充 fillchar = none ,也可以用指定字符来填充
S.center(width[, fillchar]) -> string
Return S centered in a string of length width. Padding is
done using the specified fill character (default is a space)
例如：
i1 = "xuexipython"
i2 = i1.center(19,'#')
print (i2)
---####xuexipython#### ----用“#”来填充
4、upper(self): # real signature unknown; restored from __doc__
""" 把字符串转换为大写
S.upper() -> string
Return a copy of the string S converted to uppercase.
5、lower(self): # real signature unknown; restored from __doc__
"""把字符串转换为小写
S.lower() -> string
Return a copy of the string S converted to lowercase.
6、index(self, sub, start=None, end=None): # real signature unknown; restored from __doc__
""" 查找字符串中，指定字符开始的位置，star,end 默认值为空，在整个字符串中进行查找，也可指定字符中起始位置。
功能类似于:find
区别在于index 在查找时，查询不到结果时报错，ValueError: substring not found
find 在查找时，查询不到结果时不会报错，‘-1’
S.index(sub [,start [,end]]) -> int
Like S.find() but raise ValueError when the substring is not found.
例如：
i1 = "xuexipython"
print (i1.index('xi'))
----‘xi’字符在 "xuexipython"中在第几位置，3
7、 find(self, sub, start=None, end=None): # real signature unknown; restored from __doc__
"""查找字符串中，指定字符开始的位置，star,end 默认值为空，在整个字符串中进行查找，也可指定字符中起始位置。
S.find(sub [,start [,end]]) -> int
Return the lowest index in S where substring sub is found,
such that sub is contained within S[start:end]. Optional
arguments start and end are interpreted as in slice notation.
8、endswith(self, suffix, start=None, end=None): # real signature unknown; restored from __doc__
""" endswith() 方法用于判断字符串是否以指定后缀结尾，如果以指定后缀结尾返回True，否则返回False。可选参数"start"与"end"为检索字符串的开始与结束位置。
S.endswith(suffix[, start[, end]]) -> bool
Return True if S ends with the specified suffix, False otherwise.
With optional start, test S beginning at that position.
With optional end, stop comparing S at that position.
suffix can also be a tuple of strings to try.
例如：
i1 = "xuexipython"
print (i1.endswith('n'))
返回值：true
print (i1.endswith('i',0,5))
返回值：true
9、format(self, *args, **kwargs): # known special case of str.format
"""格式化 只能从0开始
S.format(*args, **kwargs) -> string
Return a formatted version of S, using substitutions from args and kwargs.
The substitutions are identified by braces ('{' and '}').
例如：
i1 = "xuexipython,{0},{1}"
print (i1.format('age','tt'))
返回值：xuexipython,age,tt
10、isalnum(self): # real signature unknown; restored from __doc__
"""是判断 self 是否有字符或数字
S.isalnum() -> bool
Return True if all characters in S are alphanumeric
and there is at least one character in S, False otherwise.
例如：
i1 = "xuexipython"
i2 = "test230"
i3 = " "
print (i1.isalnum())
print (i2.isalnum())
print (i3.isalnum())
返回值：
True
True
False
11、isalpha(self): # real signature unknown; restored from __doc__
"""判断self中的值是否全为字符
S.isalpha() -> bool
Return True if all characters in S are alphabetic
and there is at least one character in S, False otherwise.
例如：
i1 = "xuexipython"
i2 = "test230"
i3 = " "
print (i1.isalpha())
print (i2.isalpha())
print (i3.isalpha())
返回值：
True
False
False
12、isspace(self): # real signature unknown; restored from __doc__
""" 判断self字符串是不是都为空格，
S.isspace() -> bool
Return True if all characters in S are whitespace
and there is at least one character in S, False otherwise.
例如：
i1 = "xuexipython "
i2 = " test230"
i3 = " "
print (i1.isspace())
print (i2.isspace())
print (i3.isspace())
返回值：
False
False
True
13、 lstrip str.lstrip([chars])
lstrip() 方法用于截掉字符串左边的空格或指定字符，或指定的字符串
例如：
i1 = "xuexipython"
print (i1.lstrip('x'))
返回：uexipython
14、 rstrip str.rstrip([chars])
lstrip() 方法用于截掉字符串左边的空格或指定字符，或指定的字符串
例如：
i1 = "xuexipython"
print (i1.rstrip('n'))
返回：xuexipytho
15、strip str.strip([chars])
strip() 方法用于截掉字符串两边的空格。
16、ljust(self, width, fillchar=None): # real signature unknown; restored from __doc__
"""字符靠左对齐，不够补齐，默认为空格
S.ljust(width[, fillchar]) -> string
Return S left-justified in a string of length width. Padding is
done using the specified fill character (default is a space).
例如：
i1 = "xuexipython"
print (i1.ljust(20,'#'))
返回：xuexipython#########
17、rjust(self, width, fillchar=None): # real signature unknown; restored from __doc__
"""字符靠右对齐，不够补齐，默认为空格，同ljust正好相反
S.rjust(width[, fillchar]) -> string
Return S right-justified in a string of length width. Padding is
done using the specified fill character (default is a space)
18、replace(self, old, new, count=None): # real signature unknown; restored from __doc__
"""替换字符串中的字符为新的字符。
S.replace(old, new[, count]) -> string
Return a copy of string S with all occurrences of substring
old replaced by new. If the optional argument count is
given, only the first count occurrences are replaced.
例如：
i1 = 'xuexipython'
reg = i1.replace('xi','XI')
print (reg)
返回值：xueXIpython