python追加字典到列表

Question

根据 this post，如果我想引用一个在循环中更新的字典(而不是总是引用同一个字典)，我需要在字典上使用 .copy() 。但是，在我下面的代码示例中，这似乎不起作用:

main.py:

import collections
import json

nodes_list = ['donald', 'daisy', 'mickey', 'minnie']
edges_list = [('donald', 'daisy', '3'), ('mickey', 'minnie', '3'), ('daisy', 'minnie', '2')]
node_dict, edge_dict = collections.defaultdict(dict), collections.defaultdict(dict)
ultimate_list = []


for n in nodes_list:
    node_dict["data"]["id"] = str(n)
    ultimate_list.append(node_dict.copy())

for e in edges_list:
    edge_dict["data"]["id"] = str(e[2])
    edge_dict["data"]["source"] = e[0]
    edge_dict["data"]["target"] = e[1]
    ultimate_list.append(edge_dict.copy())

print(json.dumps(ultimate_list, indent=2))

结果我得到以下信息:

[
  {
    "data": {
      "id": "minnie"
    }
  },
  {
    "data": {
      "id": "minnie"
    }
  },
  {
    "data": {
      "id": "minnie"
    }
  },
  {
    "data": {
      "id": "minnie"
    }
  },
  {
    "data": {
      "target": "minnie",
      "id": "2",
      "source": "daysi"
    }
  },
  {
    "data": {
      "target": "minnie",
      "id": "2",
      "source": "daysi"
    }
  },
  {
    "data": {
      "target": "minnie",
      "id": "2",
      "source": "daysi"
    }
  }
]

而我实际上希望得到这个:

[
  {
    "data": {
      "id": "donald"
    }
  },
  {
    "data": {
      "id": "daisy"
    }
  },
  {
    "data": {
      "id": "mickey"
    }
  },
  {
    "data": {
      "id": "minnie"
    }
  },
  {
    "data": {
      "target": "donald",
      "id": "3",
      "source": "daysi"
    }
  },
  {
    "data": {
      "target": "mickey",
      "id": "3",
      "source": "minnie"
    }
  },
  {
    "data": {
      "target": "minnie",
      "id": "2",
      "source": "daysi"
    }
  }
]

谁能告诉我我做错了什么？

Answer 1

dict.copy 只对字典进行浅拷贝，永远不会复制嵌套字典，您需要深层复制才能将那些也复制过来。

但是，您可以简单地在循环的每次迭代中定义每个新字典，然后在该迭代中 append 新字典:

for n in nodes_list:
    node_dict = collections.defaultdict(dict) # create new instance of data structure
    node_dict["data"]["id"] = str(n)
    ultimate_list.append(node_dict)

同样适用于 edge_dict:

for e in edges_list:
    edge_dict = collections.defaultdict(dict)
    ...
    ultimate_list.append(edge_dict)