##代码
[root@room1pc01 data]# cat login1.py
#!/usr/bin/env python2.6

username = raw_input('username:')
password = raw_input('password:')


if username == 'bob':
 if password == '123456':
 print 'Login success.'
 else:
 print 'Your password error.'
else:
 print 'Your username error.'
##运行效果
[root@room1pc01 data]# python login1.py
username:bob
password:123456 ##密码明文回显在屏幕上，不安全
Login success.

##代码
[root@room1pc01 data]# cat login2.py 
#!/usr/bin/env python2.6
import getpass


username = raw_input('username:')
password = getpass.getpass('password:')

if username == 'bob':
 if password == '123456':
 print 'Login success.'
 else:
 print 'Your password error.'
else:
 print 'Your username error.'

##运行效果
[root@room1pc01 data]# python login2.py
username:bob
password: ##密码没有在屏幕上回显，私密信息得到保障
Login success.