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我的代码如下（我不知道为什么它没有缩进）：

def move_joker_2(deck):

#start checking every card in the deck until the position of 
#JOKER2 is found

#we start from position 0
position = 0

while deck [position] != JOKER2:
    position = position + 1

#the new position for JOKER2
if position < len (deck) - 3:
    new_position = position + 2
elif position == len (deck) - 2:
    new_position = 0
else:
    new_position = 1

#to reorganize deck, we need 2 things
# 1.) a list of the cards above JOKER2 after moving the cards
# 2.) a list of the cards below JOKER2 after moving the cards

#depending of new_position, there are 3 possible new decks

if new_position == 0:
    #no cards above, JOKER2 will become the top card
    cards_above = []
    #every other card will be below it
    cards_below = deck
    #remove JOKER2, since we moved it
    cards_below.pop(position)

elif new_position == 1:
    #the only card above JOKER2 will be the top card
    cards_above = [deck[0]]     

    #every other card up except the last one will be below it
    cards_below = deck [new_position:len(deck)-1]

else:   

    cards_above = deck[0:new_position+1]    
    #remove JOKER2, since we moved it
    cards_above.pop(position)
    cards_below = deck [new_position+1:]

#final deck
deck = cards_above + [JOKER2] + cards_below

我的代码收到一个字符串列表并最终对其进行变异...

但是为什么它不改变原来的列表呢？例如：

甲板 = [1, 3, 27, 8, 9] move_joker_2(甲板)

考虑到 JOKER2 是 27，它应该将列表更改为： [1, 3, 8, 9, 27]

但是每当我打电话给deck时，它都没有改变......

4

2 回答 2

6

deck = cards_above + [JOKER2] + cards_below不改变deck.

它创建一个新列表并deck引用该新列表。

要更改桌面的内容，请使用切片符号，如deck[:] = cards_above + [JOKER2] + cards_below.

>>> def f1(deck):
...     deck = [1,2,3] # This does not change the `deck` passed.
                       # This just create a local variable `deck`.
...
>>> def f2(deck):
...     deck[:] = [4,5,6] # This change the `deck` passed.
...
>>> deck = [0]
>>> f1(deck)
>>> deck
[0]
>>> f2(deck)
>>> deck
[4, 5, 6]
于 2013-10-27T07:18:38.377 回答
1

deck作为参数传递只是一个带有引用副本的变量，所以当你分配

deck = ....

you create the new object and assign its reference to the deck variable. These are not references in the c++ sense, these are always copies of references.

One opssible walkaround would be to use

deck[:] = ...

which updates the content of the object, not just the reference value

于 2013-10-27T07:19:50.800 回答