Make the Python json encoder support Python's new dataclasses

问题

Starting with Python 3.7, there is something called a dataclass:

from dataclasses import dataclass

@dataclass
class Foo:
    x: str

However, the following fails:

>>> import json
>>> foo = Foo(x="bar")
>>> json.dumps(foo)
TypeError: Object of type Foo is not JSON serializable

How can I make json.dumps() encode instances of Foo into json objects?

回答1:

Much like you can add support to the JSON encoder for datetime objects or Decimals, you can also provide a custom encoder subclass to serialize dataclasses:

import dataclasses, json

class EnhancedJSONEncoder(json.JSONEncoder):
        def default(self, o):
            if dataclasses.is_dataclass(o):
                return dataclasses.asdict(o)
            return super().default(o)

json.dumps(foo, cls=EnhancedJSONEncoder)

回答2:

Can't you just use the dataclasses.asdict() function to convert the dataclass to a dict? Something like:

>>> @dataclass
... class Foo:
...     a: int
...     b: int
...     
>>> x = Foo(1,2)
>>> json.dumps(dataclasses.asdict(x))
'{"a": 1, "b": 2}'

回答3:

If you are ok with using a library for that, you can use dataclasses-json. Here is an example:

from dataclasses import dataclass

from dataclasses_json import dataclass_json


@dataclass_json
@dataclass
class Foo:
    x: str


foo = Foo(x="some-string")
foo_json = foo.to_json()

It also supports embedded dataclasses - if your dataclass has a field typed as another dataclass - if all dataclasses envolved have the @dataclass_json decorator.

来源：https://stackoverflow.com/questions/51286748/make-the-python-json-encoder-support-pythons-new-dataclasses

标签

python

python-dataclasses