Python字符串
字符串或串(String)是由数字、字母、下划线组成的一串字符。
一般记为 :

s="a1a2···an"(n>=0)

它是编程语言中表示文本的数据类型。
python的字串列表有2种取值顺序:

• 从左到右索引默认0开始的，最大范围是字符串长度少1
• 从右到左索引默认-1开始的，最大范围是字符串开头
• 如果你的实要取得一段子串的话，可以用到变量[头下标:尾下标]，就可以截取相应的字符串，其中下标是从0开始算起，可以是正数或负数，下标可以为空表示取到头或尾。

比如:

s = 'ilovepython'

s[1:5]的结果是love。
当使用以冒号分隔的字符串，python返回一个新的对象，结果包含了以这对偏移标识的连续的内容，左边的开始是包含了下边界。
上面的结果包含了s[1]的值l，而取到的最大范围不包括上边界，就是s[5]的值p。
加号（+）是字符串连接运算符，星号（*）是重复操作。如下实例：

#!/usr/bin/python# -*- coding: UTF-8 -*-str = 'Hello World!'print str # 输出完整字符串print str[0] # 输出字符串中的第一个字符print str[2:5] # 输出字符串中第三个至第五个之间的字符串print str[2:] # 输出从第三个字符开始的字符串print str * 2 # 输出字符串两次print str + "TEST" # 输出连接的字符串

以上实例输出结果：

Hello World!Hllollo World!Hello World!Hello World!Hello World!TEST

Python比较运算符
以下假设变量a为10，变量b为20：

以下实例演示了Python所有比较运算符的操作：

#!/usr/bin/pythona = 21b = 10c = 0if ( a == b ): print "Line 1 - a is equal to b"else: print "Line 1 - a is not equal to b"if ( a != b ): print "Line 2 - a is not equal to b"else: print "Line 2 - a is equal to b"if ( a <> b ): print "Line 3 - a is not equal to b"else: print "Line 3 - a is equal to b"if ( a < b ): print "Line 4 - a is less than b" else: print "Line 4 - a is not less than b"if ( a > b ): print "Line 5 - a is greater than b"else: print "Line 5 - a is not greater than b"a = 5;b = 20;if ( a <= b ): print "Line 6 - a is either less than or equal to b"else: print "Line 6 - a is neither less than nor equal to b"if ( b >= a ): print "Line 7 - b is either greater than or equal to b"else: print "Line 7 - b is neither greater than nor equal to b"

以上实例输出结果：

Line 1 - a is not equal to bLine 2 - a is not equal to bLine 3 - a is not equal to bLine 4 - a is not less than bLine 5 - a is greater than bLine 6 - a is either less than or equal to bLine 7 - b is either greater than or equal to b