如何将输入添加到空列表并保存它？

Question

我试着为游戏中的项目建立一个列表，我不得不在我的程序中多次调用它。我注意到输入并没有存储在我的列表中，它每次都会替换它。你知道吗

我使用了playeritems.append()和playeritems.extend()，但不起作用。你知道吗

def addbackpack():
    global playeritems
    gameitems= ["sword", "potion"]
    playeritems = []
    print ("\nWhat would you like to add to your backpack? The sword or potion?\n")
    p1_additem = str(input())
    if p1_additem in gameitems:
        playeritems.append(p1_additem)
        print ("\nYou added",p1_additem,"to your backpack.\n")
    else:
        print ("\nThat is not a choice!\n")
        return addbackpack()

addbackpack()
print (playeritems)
addbackpack()
print (playeritems)

这是我第一次输入剑，第二次输入药剂后的准确结果：

What would you like to add to your backpack? The sword or potion?

sword

You added sword to your backpack

['sword']

What would you like to add to your backpack? The sword or potion?

potion

You added potion to your backpack

['potion'] 

Answer 1

它确实可以工作（因为每个新项都会被添加），但是每次对addbackpack的调用都会重新初始化playeritems，删除之前在那里的所有内容。你知道吗