python字符串常用内建函数总结

自己总结一些常用字符串函数，理解比较粗糙

1.字符串内建函数-大小写转换函数

（1）str.capitalize

Help on method_descriptor:

capitalize(...)
     S.capitalize() -> str
    
     Return a capitalized version of S, i.e. make the first character
     have upper case and the rest lower case.

返回值首字母大写，其余小写，不改变数据本身

实例：

a = “start”

a.caplitalize()

Start

(2)str.title()

Help on method_descriptor:

title(...)
     S.title() -> str
    
     Return a titlecased version of S, i.e. words start with title case
     characters, all remaining cased characters have lower case

返回值首字母大写，其余都小写

实例：

a = “start”

a.title()

Start

a = “sTART”

a.title()

Start

（3）str.lower()

Help on method_descriptor:

lower(...)
     S.lower() -> str
    
     Return a copy of the string S converted to lowercase.

返回值字母大写转换为小写，大转小

实例:

a = “START”

a.lower()

start

(4)str.upper()

Help on method_descriptor:

upper(...)
     S.upper() -> str
    
     Return a copy of S converted to uppercase.

返回值字母小写转换为大写，小转大

实例：

a = “start”

a.upper()

START

(5)str.swapcase()

Help on method_descriptor:

swapcase(...)
     S.swapcase() -> str
    
     Return a copy of S with uppercase characters converted to lowercase
     and vice versa.

返回值字母大写转换成小写，小写转换成大写

实例：

a = “Start”

a.swapcase()

sTART

2.字符串内建函数-搜索函数

（1）str.find()

Help on method_descriptor:

find(...)
     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.
    
     Return -1 on failure.

S.find(sub[, start[, end]])

搜索字符串在指定的索引范围是否包含子字符串的索引值，否则返回-1

参数:

sub –指定索引的字符串

start -- 开始索引，默认为0。

end -- 结束索引，默认为字符串的长度

实例：

a = “start”

b = “hd”

c = “ar”

a.find(b)

-1

a.find(c)

2

(2)str.index()

Help on method_descriptor:

index(...)
     S.index(sub[, start[, end]]) -> int
    
     Like S.find() but raise ValueError when the substring is not found.

搜索字符串在指定的索引范围是否包含子字符串的索引值,与find方法一样，只不过如果str不在字符串中回报一个异常

实例：

a = “start”

b = “hd”

c = “ar”

a.index(b)

Traceback (most recent call last):
   File "<stdin>", line 1, in <module>

ValueError: substring not found

a.index(c)

2

(3)str.count()

Help on method_descriptor:

count(...)
     S.count(sub[, start[, end]]) -> int
    
     Return the number of non-overlapping occurrences of substring sub in
     string S[start:end].  Optional arguments start and end are
     interpreted as in slice notation.

计算子字符串在指定字符串中出现的次数

实例：

a = “start”

b = “a”

a.count(b)

1

(4)str.endswith()

Help on method_descriptor:

endswith(...)
     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.

如果字符串含有指定的后缀返回True，否则返回False

实例：

a = “start”

b = “a”

a.endswith(b)

False

a = “start”

b = “t”

a.endswith(b)

True

3.字符串内建函数-替换函数

(1)str.replace(old,new)

Help on method_descriptor:

replace(...)
     S.replace(old, new[, count]) -> str
    
     Return a copy of S with all occurrences of substring
     old replaced by new.  If the optional argument count is
     given, only the first count occurrences are replaced.

将old替换为new

实例：

a = “start”

b = “op’

a.replace(‘art’, b)

‘stop’

(2)str.strip(char)

Help on method_descriptor:

strip(...)
     S.strip([chars]) -> str
    
     Return a copy of the string S with leading and trailing
     whitespace removed.
     If chars is given and not None, remove characters in chars instead.

在str的开头和结尾删除char，当char为空时，默认删除空白符

实例：

a = “   start   ”

a.strip()

“start”

(3)str.rstrip()

Help on method_descriptor:

rstrip(...)
     S.rstrip([chars]) -> str
    
     Return a copy of the string S with trailing whitespace removed.
     If chars is given and not None, remove characters in chars instead.

删除str字符串末尾的空格，或换行符号

实例：

a = “ start  ”

a.rstrip()

“  start”