python - 使用输入列表中的字典元素附加到元组列表

Question

我有两个这样的列表:

my_list = [['can you change departure date to 30th March', '207443006734608218498'], ['can you downgrade to economy class?', '276566920664343421717'], ['book flight from San Francisco to Los Angeles on April 17-24', '897058868855606085615']]

ids_list = ['207443006734608218498', '276566920664343421717', '897058868855606085615']

我检查 my_list 中匹配的元素的 ids_list 然后我尝试追加到其他列表

我试着得到像那个最终列表:

[
  ('can you change departure date to 30th March',
  {
    'ids': {
      '207443006734608218498': 'True',
      '276566920664343421717': 'False',
      '897058868855606085615': 'False'
    }
  }),
  ('can you downgrade to economy class?',
  {
    'ids': {
      '207443006734608218498': 'False',
      '276566920664343421717': 'True',
      '897058868855606085615': 'False'
    }
  }),
  ('book flight from San Francisco to Los Angeles on April 17-24',
  {
    'ids': {
      '207443006734608218498': 'False',
      '276566920664343421717': 'False',
      '897058868855606085615': 'True'
    }
  })
]

为此我编写了简单的循环并像那样更新字典的元组

>>> data = {} 
>>> for x in my_list:
...     for y in ids_list:
...             data.update({y: "True"} if x[1]==y  else {y: "False"})
...     print((x[0],{"ids": data}))
... 

('can you change departure date to 30th March', {'ids': {'207443006734608218498': 'True', '276566920664343421717': 'False', '897058868855606085615': 'False'}})
('can you downgrade to economy class?', {'ids': {'207443006734608218498': 'False', '276566920664343421717': 'True', '897058868855606085615': 'False'}})
('book flight from San Francisco to Los Angeles on April 17-24', {'ids': {'207443006734608218498': 'False', '276566920664343421717': 'False', '897058868855606085615': 'True'}})

但是当我在列表中追加时，数据字典附加了错误的值，当我打印时，数据字典的值是正确的我应该做错什么？

>>> t = []
>>> for x in my_list:
...     for y in ids_list:
...             data.update({y: "True"} if x[1]==y  else {y: "False"})
...     t.append((x[0],{"ids":data}))
... 
>>> t
    [
 ('can you change departure date to 30th March', {'ids': {'207443006734608218498': 'False', '276566920664343421717': 'False', '897058868855606085615': 'True'}}),
 ('can you downgrade to economy class?', {'ids': {'207443006734608218498': 'False', '276566920664343421717': 'False', '897058868855606085615': 'True'}}), 
 ('book flight from San Francisco to Los Angeles on April 17-24', {'ids': {'207443006734608218498': 'False', '276566920664343421717': 'False', '897058868855606085615': 'True'}})]

Answer 1

问题是这一行:

data.update({y: "True"} if x[1]==y  else {y: "False"})

它就地更新数据，而不是将名称重新绑定(bind)到新的字典对象。为了更好地理解，让我们看看通过“展开”你的循环真正放入 t 的内容:

t = [(my_list[0][0], {'ids': data}), (my_list[1][0], {'ids': data}), (my_list[2][0], {'ids': data})]

请注意，虽然外部字典(带有 'ids')每次都是不同的对象，但内部字典始终是对同一 data 对象的引用。您对 data 所做的任何更改都将在列表中的每个元素中可见。

解决方案当然是在循环的每次迭代中创建一个新对象。我能想到的最简单的方法是将您的内部循环变成字典理解:

t = []
for x in my_list:
    data = {id: "True" if x[1] == id  else "False" for id in ids}
    t.append((x[0], {"ids": data}))

您可以进行的另一项改进是解包 x 以使代码更易读:

t = []
for request, id in my_list:
    data = {x: "True" if id == x  else "False" for x in ids}
    t.append((request, {"ids": data}))

最后，如果您愿意，您的整个代码足够简单，可以坚持使用单行列表推导式:

t = [(request, {"ids": {x: "True" if id == x  else "False" for x in ids}}) for request, id in my_list]