if...else循环

例子1 用户输入判断

# 提示输入用户名和密码

# 验证用户名和密码
#     如果错误，则输出用户名或密码错误
#     如果成功，则输出 欢迎，XXX!

import getpass                #调用getpass模块
username = input("username:")
passwd = getpass.getpass("passwd:")   #get.getpass实现密码不显示的效果

_username = 'gui'
_passwd = "123"

if username == _username and passwd ==_passwd:
    print("Welcome to {name} login...".format(name=username))
else:
    print("invalid username or passwd")

例子2 猜年龄游戏

# 真实年龄是56

# 提示输入年龄
# 验证年龄
#   如果正确，输出"You got it"
#   如果年龄偏大，输出"Think smaller!"
#   如果年龄偏小，输出"Think bigger!"


age_of_oldboy = 56
guess_age = int(input("guess age:"))  

if guess_age == age_of_oldboy:
    print("You got it")
elif guess_age > age_of_oldboy:
    print("Think smaller!")
else:
    print ("Think bigger!")