Override default JSON encoder to add support for dataclasses

encoder.py

import json
from dataclasses import dataclass, is_dataclass, asdict


class DataclassEncoder(json.JSONEncoder):
    def default(self, obj):
        if is_dataclass(obj):
            return asdict(obj)
        return super().default(obj)


@dataclass
class MyData:
    foo: int


# Monkeypatch the stdlib
# This is extremely bad practice and may break your application in unexpected
# ways.  Use at your own risk.
json._default_encoder = DataclassEncoder(
    skipkeys=False,
    ensure_ascii=True,
    check_circular=True,
    allow_nan=True,
    indent=None,
    separators=None,
    default=None,
)


print(json.dumps(MyData(foo=1)))
# Output:  {"foo": 1}