python - 有条件地用两个列表替换项目

Question

我试图用同一索引中列表 B 中的元素替换列表 A 中的任何“-”实例。现在我的输出根本不修改列表 A，所以我怀疑我的 for 循环正在使用副本。

A = [ ["dog", ["corgi",'-',"labrador"]], ["cat", ["tabby","persian",'-']] ]
B = ["BLANK 1","BLANK 2","BLANK 3"]
i = 0
for one,two in zip(A[i][1],B):
    if one == '-':
        one = two
    i += 1
print(A)

我希望我的输出(即修改后的列表 A)如下所示:

[ ["dog", ["corgi","BLANK 2","labrador"]], ["cat", ["tabby","persian","BLANK 3"]] ] 

非常感谢你们给我的任何指导!

Answer 1

为了执行如此复杂的操作，我们可以将其分解为更简单的操作。在最简单的层面上，我们希望用另一个字符串替换破折号 (-):

>>> x = 'corgi'
>>> y = 'BLANK 1'
>>> x if x != '-' else y
corgi

>>> x = '-'
>>> y = 'BLANK 2'
>>> x if x != '-' else y
BLANK 2

下一步是将 ["corgi",'-',"labrador"] 替换为 ["corgi",'BLANK 2',"labrador"]:

>>> breed = ["corgi",'-',"labrador"]
>>> B = ["BLANK 1","BLANK 2","BLANK 3"]
>>> zip(breed, B)
[('corgi', 'BLANK 1'), ('-', 'BLANK 2'), ('labrador', 'BLANK 3')]
>>> [x if x != '-' else y for x, y in zip(breed, B)]
['corgi', 'BLANK 2', 'labrador']

最后，我们来看看大局:

>>> C = [ [animal,
      [x if x != '-' else y for x, y in zip(breed, B)] ]
      for animal, breed in A]

>>> print C
[['dog', ['corgi', 'BLANK 2', 'labrador']], ['cat', ['tabby', 'persian', 'BLANK 3']]]