from random import choice

rules = {'rock': 'paper', 'scissors': 'rock', 'paper': 'scissors'}
previous = ['rock', 'paper', 'scissors']

while True:
    human = input('\nchoose your weapon: ')
    computer = rules[choice(previous)]  # choose the weapon which beats a randomly chosen weapon from "previous"

    if human in ('quit', 'exit'): break

    elif human in rules:
        previous.append(human)
        print('the computer played', computer, end='; ')

        if rules[computer] == human:  # if what beats the computer's choice is the human's choice...
            print('yay you win!')
        elif rules[human] == computer:  # if what beats the human's choice is the computer's choice...
            print('the computer beat you... :(')
        else: print("it's a tie!")

    else: print("that's not a valid choice")