def passwordnumbercheck(password):
    numberCheck = [];
    for i in password:
        numberCheck.append(i.isnumeric());
    if numberCheck == [False, False, True, False]:
        return True;
        print ("this is a valid password")
    else:
        return False;
        print ("this is invalid")


def passwordlettercheck(password):
    letterCheck = [];
    for i in password:
        letterCheck.append(i.isalpha());
    if letterCheck == [True, True, False, True]:
        return True;
        passwordnumbercheck (password)
    else:
        return False;
        print("this is not a valid password")



password = input("enter a valid password, it must be a letter, a letter, a number and a letter ")
passwordlettercheck (password)
passwordnumbercheck (password)