Make the Python json encoder support Python's new dataclasses

python python-dataclasses
miracle2k picture miracle2k · Jul 11, 2018 · Viewed 34.8k times · Source

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?

Answer

miracle2k picture miracle2k · Jul 11, 2018

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)

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