字符串是一种特殊的tuple,支持部分tuple的运算符
>>> a ='12345'
>>> a[2]
'3'
>>> a[3:]
'45'
>>> type(a)
<class'str'>
>>> a*2
'1234512345'
>>>6in a
Traceback(most recent call last):
File"", line 1,in
TypeError:'in ' requires stringas left operand,notint
>>> a
'12345'
>>>for x in a:print(x)
...
1
2
3
4
5
