python的问题：我如何使某些事情只在调用定义的时候发生？

Question

因此，我有一个文本冒险游戏的intr计算机科学类&；我需要把东西放进去。在定义中，我有一个全局变量刀。但是我需要这样做，这样它就不会在你每次走进房间（或者需要定义）时要求你拿起刀，如果你已经拿起了刀

    global knife
    global knife_val
    if knife_val = 1
        knife = input("You step on the handle of a knife when walking into the room. Do you wish to pick it up?").lower()
        if knife == "yes":
            print("You picked up the Knife!")
            knife_val = 0

后来它问你

        attack = input("Do you wish to attack?")
        if attack == "yes":
            move_miss = random.randint(1,5)
            if move_miss == 1:
                miss = True
            else:
                miss = False
            if miss:
                print("You missed!")
                print("You are bitten by the monster and you die. Goodbye")
                quit()
            elif attack == "no":
                print("You are bitten by the monster and you die. Goodbye")
                quit()
            print("You beat the monster!")
    elif knife_val = 1:
            print("You are bitten by the monster and you die. Goodbye")
            quit()

我如何才能使其仅在满足条件时发生？当我尝试之前，有一个错误