python学习笔记3.1.3x 之字符串

 Python中的字符串被定义为引号之间的字符集合，可是使用单引号爽引号，三引号（三个联系的单引号或者栓引号，可以用来表示特殊字符。
 
索引操作符（[]）以及 切片操作符（[:]）可以得到子字符串，第一个字符的索引为0 最后一个为 -1

ActivePython 3.1.3.5 (ActiveState Software Inc.) based on
Python 3.1.3 (r313:86834, Dec  3 2010, 13:32:40) [MSC v.1500 32 bit (Intel)] on win32
Type "copyright", "credits" or "license()" for more information.
>>> s1='python'
>>> s2='is good'
>>> s1[0]
'p'
>>> s1[2:5]
'tho'
>>> s2[:2]
'is'
>>> s2[3:]
'good'
>>> s2[:-2]
'is go'
>>> s1[-1]
'n'
>>> s1[:-1]
'pytho'
>>> s1*2
'pythonpython'
>>> s1+''s2
SyntaxError: invalid syntax
>>> s1+''+s2 #''之间没有空格
'pythonis good' 
>>> s1+' '+s2 #''之间有空格
'python is good'