#!/usr/bin/env python
#codingutf-8
count = 0
while count < 3:
    username = raw_input("USERNAME:")
    password = raw_input("PASSWORD:")
    if username == "user" and password == "123":
        print "welcome!!!"
        break
    elif username != "user" and password != "123":
        print "username or password wrong!!!"
    elif username == "user" and password != "123":
        print "password is wrong!!!"
    elif username != "user" and password == "123":
        print "username or password is wrong!!!"
    count +=1
    if count == 3:
        print "go away ang don‘t back!!!"

Python 练习1