username = input("please enter user name: ")
password = input("please enter password: ")

def wholestring(stuff):
    str.isalnum(stuff)

def validate(username, password):
    if username == password:
        return False
    passlength = len(password)
    if passlength < 8:
        return False
    wholestring(password)
    wholestring(username)

def main():
    if validate(username,password) == True:
        print("Password is valid")
    else:
        print("Password is invalid")

main()