特性：不可修改
name.capitalize() 首字母大写
name.casefold() 大写全部变小写
name.center(50,"-") 输出 '---------------------Alex Li----------------------'
name.count('lex') 统计 lex出现次数
name.encode() 将字符串编码成bytes格式
name.endswith("Li") 判断字符串是否以 Li结尾
"Alex\tLi".expandtabs(10) 输出'Alex Li'， 将\t转换成多长的空格
name.find('A') 查找A,找到返回其索引， 找不到返回-1
format :
>>> msg = "my name is {}, and age is {}"
>>> msg.format("alex",22)
'my name is alex, and age is 22'
>>> msg = "my name is {1}, and age is {0}"
>>> msg.format("alex",22)
'my name is 22, and age is alex'
>>> msg = "my name is {name}, and age is {age}"
>>> msg.format(age=22,name="ale")
'my name is ale, and age is 22'
format_map
>>> msg.format_map({'name':'alex','age':22})
'my name is alex, and age is 22'
msg.index('a') 返回a所在字符串的索引
'9aA'.isalnum() True
'9'.isdigit() 是否整数
name.isnumeric
name.isprintable
name.isspace
name.istitle
name.isupper
"|".join(['alex','jack','rain'])
'alex|jack|rain'
maketrans
>>> intab = "aeiou" #This is the string having actual characters.
>>> outtab = "12345" #This is the string having corresponding mapping character
>>> trantab = str.maketrans(intab, outtab)
>>>
>>> str = "this is string example....wow!!!"
>>> str.translate(trantab)
'th3s 3s str3ng 2x1mpl2....w4w!!!'
msg.partition('is') 输出 ('my name ', 'is', ' {name}, and age is {age}')
>>> "alex li, chinese name is lijie".replace("li","LI",1)
'alex LI, chinese name is lijie'
msg.swapcase 大小写互换
>>> msg.zfill(40)
'00000my name is {name}, and age is {age}'
>>> n4.ljust(40,"-")
'Hello 2orld-----------------------------'
>>> n4.rjust(40,"-")
'-----------------------------Hello 2orld'
>>> b="ddefdsdff_哈哈"
>>> b.isidentifier() #检测一段字符串可否被当作标志符，即是否符合变量命名规则
True
