十七：字符串操作

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.isprintablename.isspacename.istitlename.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