s="a1a2···an"(n>=0)

s = 'ilovepython'

#!/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

Hello World!
H
llo
llo World!
Hello World!Hello World!
Hello World!TEST

#!/usr/bin/python

a = 21
b = 10
c = 0

if ( 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"

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