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bpo-35540 dataclasses.asdict now supports defaultdict fields (pythong…
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kwsp authored Oct 7, 2022
1 parent a4b7794 commit c46a423
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Showing 3 changed files with 28 additions and 2 deletions.
8 changes: 8 additions & 0 deletions Lib/dataclasses.py
Original file line number Diff line number Diff line change
Expand Up @@ -1325,6 +1325,14 @@ def _asdict_inner(obj, dict_factory):
# generator (which is not true for namedtuples, handled
# above).
return type(obj)(_asdict_inner(v, dict_factory) for v in obj)
elif isinstance(obj, dict) and hasattr(type(obj), 'default_factory'):
# obj is a defaultdict, which has a different constructor from
# dict as it requires the default_factory as its first arg.
# https://bugs.python.org/issue35540
result = type(obj)(getattr(obj, 'default_factory'))
for k, v in obj.items():
result[_asdict_inner(k, dict_factory)] = _asdict_inner(v, dict_factory)
return result
elif isinstance(obj, dict):
return type(obj)((_asdict_inner(k, dict_factory),
_asdict_inner(v, dict_factory))
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21 changes: 19 additions & 2 deletions Lib/test/test_dataclasses.py
Original file line number Diff line number Diff line change
Expand Up @@ -12,9 +12,9 @@
import weakref
import unittest
from unittest.mock import Mock
from typing import ClassVar, Any, List, Union, Tuple, Dict, Generic, TypeVar, Optional, Protocol
from typing import ClassVar, Any, List, Union, Tuple, Dict, Generic, TypeVar, Optional, Protocol, DefaultDict
from typing import get_type_hints
from collections import deque, OrderedDict, namedtuple
from collections import deque, OrderedDict, namedtuple, defaultdict
from functools import total_ordering

import typing # Needed for the string "typing.ClassVar[int]" to work as an annotation.
Expand Down Expand Up @@ -1677,6 +1677,23 @@ class C:
self.assertIsNot(d['f'], t)
self.assertEqual(d['f'].my_a(), 6)

def test_helper_asdict_defaultdict(self):
# Ensure asdict() does not throw exceptions when a
# defaultdict is a member of a dataclass

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


dd = defaultdict(list)
dd["x"].append(12)
c = C(mp=dd)
d = asdict(c)

assert d == {"mp": {"x": [12]}}
assert d["mp"] is not c.mp # make sure defaultdict is copied

def test_helper_astuple(self):
# Basic tests for astuple(), it should return a new tuple.
@dataclass
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Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
Fix :func:`dataclasses.asdict` crash when :class:`collections.defaultdict` is present in the attributes.

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