Is it possible to serialize a class without instanciating a dict? (ie: use a generator)

[nmoreaud]

Hello,
I wonder if it is possible, to serialize a class to a dict using a generator.
It could help to reduce memory allocations when serializing dataclasses with __slots__.

I think about something like this:

from dataclasses import dataclass
import json


@dataclass
class Data:
    __slots__ = ('a', 'b')

    a: int
    b: int

    def items(self):
        yield ('a', self.a)
        yield ('b', self.b)


def default(obj):
    if isinstance(obj, Data):
        return obj.items()  # ko
        # return dict(obj.items()) # OK
        # return {'toto': 'tata'}.items()  # ko


data = {"data": Data(a=1, b=2)}
j = json.dumps(data, default=default)
print(j)

[etrepum]

No, that is not currently possible. isinstance(obj, dict) must be True in order for it to serialize as a JSON object. I think it's unlikely to make all that much of a difference, but you're welcome to try it. If you can show it does improve performance in a meaningful way and provide a PR with tests then I'd be happy to review it.