username = ['mel1', 'mel2', 'mel3']
password = ['tyr1', 'tyr2', 'tyr3']

def log_sys():
    logged_in = False
    log_user = raw_input('Please type in your username: ')
    log_pass = raw_input('Please type in your password: ')

    if log_user in username:
        index = username.index(log_user)
        if log_pass == password[index]:
            logged_in = True

    if logged_in:
        print 'You are logged in'
    else:
       print 'Wrong username or password'
       log_sys()

def reg_sys(user):
    regpass1 = raw_input('Please choose a password: ')
    regpass2 = raw_input('Please retype password: ')

    if regpass1 == regpass2:
        username.append(user)
        password.append(regpass1)
        log_sys()
    else:
        print 'Passwords did not match'
        reg_sys(user)

def reglog_system():
    reglog = raw_input('Do you want to register or login?: ')

    if reglog == 'register':
        regname = raw_input('Please choose a username: ')
        reg_sys(regname)
    elif reglog == 'login':
        log_sys()
    else:
        reglog_system()

reglog_system()