How to add custom convertors for JSON serializer in Python

main.py

import dataclasses
import json
from datetime import datetime


def convertor(v):
    if isinstance(v, datetime):
        return v.timestamp()
    elif dataclasses.is_dataclass(v):
        return dataclasses.asdict(v)

    type_name = v.__class__.__name__
    raise TypeError(f"Object of type {type_name!r} is not JSON serializable")


@dataclasses.dataclass
class Bar:
    created_at: datetime = dataclasses.field(default_factory=datetime.now)


print(json.dumps(Bar(), default=convertor))
# {"created_at": 1618383433.054921}