for 循环

#print 奇数
for i in range(1,101,2) :　　# 2 为步长
    print("loop:",i)

for i in range(100):
    if i < 50 or i > 70:
        print(i)

_user = "eva"
_passwd = "123"

for i in range(3):
    username = input("Username:")
    password = input("Password:")

    if username == _user and password == _password:
        print("Welcome %s login..." %_user)
        break
    else:
        print("Invalid username or password!")