使用python向JSON添加重复键 [英] Adding duplicate keys to JSON with python

问题描述

有没有一种方法可以使用python向json添加重复密钥?

Is there a way to add duplicate keys to json with python?

据我了解，python词典中不能有重复的键.通常，创建json的方法是先创建字典，然后创建json.dumps.但是，我需要在JSON中使用重复的键进行测试.但是我不能这样做，因为我不能在python字典中添加重复的键.我正在尝试在python 3中做到这一点

From my understanding, you can't have duplicate keys in python dictionaries. Usually, how I go about creating json is to create the dictionary and then json.dumps. However, I need duplicated keys within the JSON for testing purposes. But I can't do so because I can't add duplicate keys in a python dictionary. I am trying to doing this in python 3

推荐答案

您总是可以手动构造这样的字符串值.

You could always construct such a string value by hand.

另一方面，可以使 C Python json模块对重复的密钥进行编码.在 Python 2 中，这非常有点棘手，因为json模块完全不遵循鸭嘴式输入.

On the other hand, one can make the CPython json module to encode duplicate keys. This is very tricky in Python 2 because json module does not respect duck-typing at all.

直接的解决方案是从collections.Mapping继承-很好，因为"MyMapping不是可序列化的JSON."

The straightforward solution would be to inherit from collections.Mapping - well you can't, since "MyMapping is not a JSON serializable."

下一个尝试将dict子类化-很好，但是如果json.dumps注意到类型为dict，它将跳过调用__len__并直接查看基础dict-如果它为空，{}是直接输出的，因此很明显，如果我们伪造方法，则基础字典一定不能为空.

Next one tries to subclass a dict - well, but if json.dumps notices that the type is dict, it skips from calling __len__, and sees the underlying dict directly - if it is empty, {} is output directly, so clearly if we fake the methods, the underlying dictionary must not be empty.

下一个欢乐源是实际上调用了__iter__，它会迭代键；对于每个键，都会调用__getitem__，因此我们需要记住给定键返回的对应值是什么...因此，我们得出了一个非常丑陋的Python 2解决方案:

The next source of joy is that actually __iter__ is called, which iterates keys; and for each key, the __getitem__ is called, so we need to remember what is the corresponding value to return for the given key... thus we arrive to a very ugly solution for Python 2:

import json
class FakeDict(dict):
    def __init__(self, items):
        # need to have something in the dictionary
        self['something'] = 'something'
        self.items = items

    def __getitem__(self, key):
        return self.last_val

    def __iter__(self):
        subiter = iter(self.items)
        def generator():
            for key, value in self.items:
                self.last_val = value
                yield key

        return generator()

print json.dumps(FakeDict([('a', 5), ('a', 6)]), sort_keys=False)

---

在CPython 3.3+中，它稍微容易些...否，collections.abc.Mapping不起作用，是的，您需要将dict子类化，是的，您需要伪造您的字典包含内容...但是内部JSON编码器调用items而不是__iter__和__getitem__！

---

In CPython 3.3+ it is slightly easier... no, collections.abc.Mapping does not work, yes, you need to subclass a dict, yes, you need to fake that your dictionary has content... but the internal JSON encoder calls items instead of __iter__ and __getitem__!

因此在Python 3上:

Thus on Python 3:

import json

class FakeDict(dict):
    def __init__(self, items):
        self['something'] = 'something'
        self._items = items
    def items(self):
        return self._items

print(json.dumps(FakeDict([('a', 1), ('a', 2)])))

打印出

{"a": 1, "a": 2}

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