~~~~练习~~~~用户登录（三次机会重试）

基础需求：

• 让用户输入用户名密码
• 认证成功后显示欢迎信息
• 输错三次后退出程序

count=1
PS=0
name=input("Please input your name:")
password=input("Please input your password:")
while count<=2 and PS==0:
	if name=="root" and password=="1234":
		PS=1
		print("Welcome!")
	elif count==2:
		name=input("Lasttime!Please enter :")
		password=input("Please input your password:")
		count+=1
	else:
		name=input("Wrong! Please enter again:")
		password=input("Please input your password:")
		count+=1

if count==3 and PS==0:
	print("End!!")

　　

可以支持多个用户登录

count=1    #登录次数计数位
PS=0   #登录成功标志位
name_list=['root','hao','quan']
ps_list=['123456','111','666']
name=input("Please input your name:")
password=input("Please input your password:")

while count<=3 and PS==0:
    if name in name_list:
        i=name_list.index(name)
        if (name in name_list) and (password==ps_list[i]):
            PS=1
            print("Welcome!")
        elif count<2 :
            name=input("Wrong! Please enter again:")
            password=input("Please input your password:")
            count+=1
            continue
        else :
            name=input("Lasttime!Please enter :")
            password=input("Please input your password:")
            count+=1
            continue
    elif count==2 and PS==0:
        name=input("Lasttime!Please enter :")
        password=input("Please input your password:")
        count+=1
    else:
        name=input("Wrong! Please enter again:")
        password=input("Please input your password:")
        count+=1

if count==3 and PS==0:
    print("End!!")