为什么我的函数在理论上不应该覆盖变量？ (Python 3.8)

Question

一个函数正在覆盖一个作为参数给它的变量。为什么？

这整个代码应该做什么：

创建代表卡片的对象列表（主牌组）
创建一个空列表用于存储已经从主牌组抽取的牌的 ID
从主牌组中随机选择 5 张牌并将它们添加到列表（玩家的牌组）
return 变量的临时整数列表（主牌组中卡片的 ID）

将临时列表中的项目添加到主列表

    import random

    from common import cards

    deck = cards.deck()  # creates a list of 52 class objects representing cards


    def main():
        used_cards_ids = []  # this one is being overwritten in the next step, according to the debugger

        players_deck, temp_used_cards_ids = generate_players_deck(used_cards_ids)  # this is the "next step"
        used_cards_ids.extend(temp_used_cards_ids)  # adds id of the cards which were drawn from the main deck

        print(used_cards_ids)  # prints a double list of cards ids (i.e 1, 2, 3, 4, 5, 1, 2, 3, 4, 5)


    def generate_players_deck(temp_used_cards_ids):
        players_deck = []
        counter = 0

        while counter < 5:  # until 5 cards were drawn
            cards_id = random.randint(0, 51)  # chooses a random card
            if cards_id not in temp_used_cards_ids:  # checks if the card with the same id weren't previously drawn
                counter += 1
                temp_used_cards_ids.append(cards_id)  # adds card's id to the list of drawn cards
                players_deck.append(deck[cards_id])  # adds card to the player's deck
            else:
                continue

        return players_deck, temp_used_cards_ids  # returns player's deck (list of cards objects) and list of ids of the drawn cards


    main()

Answer 1

当您将 used_cards_ids 传递给 generate_players_deck() 时，您正在向 used_cards_ids 提供 generate_players_deck() 到 append 数据的主体，您已经别名到 temp_used_cards_ids。

然后您从该函数的 return 语句中取回值，您将其存储在变量 temp_used_cards_ids 中，然后 extend temp_used_cards_ids，这实际上是 used_cards_ids，实质上改变了您两次传入的列表。

当您将列表作为函数参数传递时，您传递的不是列表的值，而是传递对原始列表的引用list. 这可能是您感到困惑的地方，或者可能是变量名和函数参数别名之间的切换。

为什么我的函数在理论上不应该覆盖变量？ (Python 3.8)

Why is my function overwriting a variable, when it's theoretically not supposed to? (Python 3.8)

python

variables

function

overwrite

python-3.x

一个函数正在覆盖一个作为参数给它的变量。为什么？