for循环使用笔记

1.for i in rang(1,101,2) #2为步长
    print("loop",i)

2.flag 标志位
3.for 循环
CODE1  for与else一起用：当for循环正常执行完循环时，则执行else语句；当for执行过程中有break后,则不执行else

_user ="wangbin"
_passwd = "123abc"
for i in range(3):
    username = input("Username:")
    password = input("Password")
    if username == _user and password == _passwd:
        print("Welcome %s login...." %_user)

        break
    else:
        print("Invalid username or password!")
else:
　　print("错误次数太多，禁止登陆")

CODE2

_user ="wangbin"
_passwd = "123abc"
passed_authentication = False
for i in range(3):
    username = input("Username:")
    password = input("Password")
    if username == _user and password == _passwd:
        print("Welcome %s login...." %_user)
        passed_authentication = True
        break
    else:
        print("Invalid username or password!")
if not passed_authentication:
print("错误次数太多，禁止登陆")