Python : defaultdict 每个值都会更新

Question

我在一个愚蠢的问题上工作了一个多小时，但我无法找出解决方案。我创建一个带有初始列表的 defaultdict(list) 并通过 for 循环更新这些列表。但是，每次我更新一个值时，所有其他值都会更新为相同的值。有人可以帮我吗？这是我的代码：

from collections import defaultdict
base = ["coucou", "salut", "tchao"]
initial_vector = [0]*len(base)
dict_vectorized_documents = defaultdict(lambda: initial_vector)
inversed_index = {"coucou": [(1, 3), (100, 4)], "salut": [(1, 1), (99, 2), (33, 3)], "tchao": [(1, 5)]}

for i, word in enumerate(base):
print(word)
for element in inversed_index[word]:
    print(element[0])
    print(i)
    print(element[1])
    print(dict_vectorized_documents[element[0]][i])
    dict_vectorized_documents[element[0]][i] = element[1]
    print(dict_vectorized_documents)

print(dict_vectorized_documents)

这是我运行时的日志：

coucou
1
0
3
0
defaultdict(<function <lambda> at 0x7fcc5fac1f28>, {1: [3, 0, 0]})
100
0
4
3
defaultdict(<function <lambda> at 0x7fcc5fac1f28>, {1: [4, 0, 0], 100:      [4, 0, 0]})
salut
1
1
1
0
defaultdict(<function <lambda> at 0x7fcc5fac1f28>, {1: [4, 1, 0], 100: [4, 1, 0]})
99
1
2
1
defaultdict(<function <lambda> at 0x7fcc5fac1f28>, {1: [4, 2, 0], 99: [4, 2, 0], 100: [4, 2, 0]})
33
1
3
2
defaultdict(<function <lambda> at 0x7fcc5fac1f28>, {1: [4, 3, 0], 99: [4, 3, 0], 100: [4, 3, 0], 33: [4, 3, 0]})
tchao
1
2
5
0

非常感谢！

Answer 1

因为您要在 defaultdict 工厂中返回 相同的列表 。最简单的解决方案？用 list:

显式复制它

>>> from collections import defaultdict
>>> base = ["coucou", "salut", "tchao"]
>>> initial_vector = [0]*len(base)
>>> dict_vectorized_documents = defaultdict(lambda: list(initial_vector))

这里是一个人为的例子，可能会更清楚：

>>> initial_list = [0, 0, 0]
>>> def get_initial():
...     return initial_list
...
>>> d = {}
>>> for k, i in zip(['key1','key2','key3'],range(3)):
...     new_list = get_initial()
...     new_list[i] = 'mutated'
...     d[k] = new_list
...
>>> d
{'key2': ['mutated', 'mutated', 'mutated'], 'key3': ['mutated', 'mutated', 'mutated'], 'key1': ['mutated', 'mutated', 'mutated']}

所以 new_list 毕竟不是新列表。但是，如果我们这样做：

>>> initial_list = [0, 0, 0]
>>> def get_initial():
...     return list(initial_list)
...
>>> d = {}
>>> for k, i in zip(['key1','key2','key3'],range(3)):
...     new_list = get_initial()
...     new_list[i] = 'mutated'
...     d[k] = new_list
...
>>> d
{'key2': [0, 'mutated', 0], 'key3': [0, 0, 'mutated'], 'key1': ['mutated', 0, 0]}
>>>

Answer 2

难道你不应该在 defaultdict 对象上追加，例如：

dict_vectorized_documents[element[0]][i].append(element[1])

Python : defaultdict 每个值都会更新

Python : defaultdict every value is updated

python

dictionary

list

defaultdict