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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”
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