Python + JSON，None 怎么了？
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Python + JSON, what happened to None?
提问by safl
Dumping and loading a dict with Noneas key, results in a dictionarywith 'null'as the key.
倾销与加载字典None的关键，结果字典与'null'作为重点。
Values are un-affected, but things get even worse if a string-key 'null'actually exists.
值不受影响，但如果字符串键'null'实际存在，情况会更糟。
What am I doing wrong here? Why can't I serialize/deserialize a dictwith Nonekeys?
我在这里做错了什么？为什么我不能dict用None键序列化/反序列化 a ？
Example
例子
>>> json.loads(json.dumps({'123':None, None:'What happened to None?'}))
{u'123': None, u'null': u'What happened to None?'}
>>> json.loads(json.dumps({'123':None, None:'What happened to None?', 'null': 'boom'}))
{u'123': None, u'null': u'boom'}
采纳答案by dan04
JSON objects are maps of stringsto values. If you try to use another type of key, they'll get converted to strings.
JSON 对象是字符串到值的映射。如果您尝试使用其他类型的键，它们将被转换为字符串。
>>> json.loads(json.dumps({123: None}))
{'123': None}
>>> json.loads(json.dumps({None: None}))
{'null': None}
回答by Dirk
According to the specification, Noneis not a valid key. It would amount to a JSON object expression, which looks like
根据规范,None不是有效的密钥。它相当于一个 JSON 对象表达式，看起来像
{ ..., null: ..., ... }
which is not valid (i.e., cannot be generated using the syntax diagram.)
这是无效的（即，不能使用语法图生成。）
Arguably, the JSON module should have raised an exception upon serialization instead of silently generating a string representation of the value.
可以说，JSON 模块应该在序列化时引发异常，而不是默默地生成值的字符串表示。
EDITJust saw, that the behaviour of the module is documented(somewhat implicitly):
编辑刚刚看到，模块的行为被记录在案（有点隐含）：
If skipkeys is True (default: False), then dict keys that are not of a basic type (str, unicode, int, long, float, bool, None) will be skipped instead of raising a TypeError.
如果 skipkeys 为 True（默认值：False），则将跳过不是基本类型（str、unicode、int、long、float、bool、None）的 dict 键，而不是引发 TypeError。
so it seems, as if this behaviour is intentional (I still find it questionable given the current JSON specification).
所以看起来，好像这种行为是故意的（鉴于当前的 JSON 规范，我仍然觉得它有问题）。
回答by Duncan MC Leod
As @dan04 shows, Noneis converted to 'null'.
正如@dan04 所示，None转换为'null'.
Everything is fine, the value is stored into the dict with
一切都很好，值存储到字典中
"null": "What happened to None?"
But then came another Key called 'null'.
但随后又出现了另一个名为 的 Key 'null'。
So the old value of the None/'null'-Key ("What happened to None?") is overwritten with "boom".
因此 None/ 'null'-Key ( "What happened to None?")的旧值被覆盖"boom"。
