1、打印0-9 十个数字

for i in range(10):
        print(i)

2、打印偶数：

for i in range(0,10,2):
        print(i)

3、if判断中猜游戏，升级(只能猜三次，超过三次没猜对，提示退出)

_age = 18

for i in range(3):
    guess_age = int(input("guess_age:"))
    if guess_age == _age:
        print("GoodLuck!")
        break
    elif guess_age > _age:
        print("cai da le ")
    else:
        print("cai xiao le ")
else:
    print("chao guo san ci qing tui chu!!!")

作业：
编写登陆接口
1.输入用户名密码；
2.认证成功后显示欢迎信息
3.输错三次，提示退出稍候在试

#!/usr/bin/env python

_user = "lijinzhu"
_pass = "123456"

for i in range(3):
    user = input("Please input your username: ")
    passwd = input("input your passwd: ")
    if _user == user and _pass == passwd:
        print("WELCOME",user,"login this system")
        break
    else:
        print("username or passwd is wrong...")
else:
    print("cuowu chaoguo 3ci,qing shaohou zai shi ......")