bpo-35540 dataclasses.asdict support defaultdict fields

[kwsp]

https://bugs.python.org/issue35540

dataclasses.asdict breaks when there are defaultdicts in the dataclass attributes because it assumes defaultdict and dict are the same thing, but in reality defaultdict takes a default_factory as the first argument in its constructor.

Since dataclasses.asdict already supports NamedTuples, I think its fair that defaultdict, which is also in the standard library, does not break dataclasses.

Test:

from dataclasses import dataclass, asdict
from typing import DefaultDict, List
from collections import defaultdict


@dataclass
class C:
    mp: DefaultDict[str, List]


dd = defaultdict(list)
dd["x"].append(12)
c = C(mp=dd)
d = asdict(c)  # throws "TypeError: first argument must be callable or None"
assert d == {"mp": {"x": [12]}}

https://bugs.python.org/issue35540

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[MaxwellDupre]

Could you add a test please?

[kwsp]

Could you add a test please?

I just added a test for this

[MaxwellDupre]

Tests ok on Fedora.
Ref to bugs.python.org/issue35540 is not future proof, assume will be turned off at some time.

[akitathai94]

Does this merge fix the issue yet cause it still throws error in Python 3.11

[kwsp]

Does this merge fix the issue yet cause it still throws error in Python 3.11

This was merged in 3.12 and not backported to 3.11

https://docs.python.org/3.12/whatsnew/changelog.html