diff --git a/Lib/dataclasses.py b/Lib/dataclasses.py index 65fb8f251861f3..bf7f290af1622f 100644 --- a/Lib/dataclasses.py +++ b/Lib/dataclasses.py @@ -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)) diff --git a/Lib/test/test_dataclasses.py b/Lib/test/test_dataclasses.py index 328dcdcb0bce78..637c456dd49e7a 100644 --- a/Lib/test/test_dataclasses.py +++ b/Lib/test/test_dataclasses.py @@ -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. @@ -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 diff --git a/Misc/NEWS.d/next/Library/2022-03-22-18-28-55.bpo-35540.nyijX9.rst b/Misc/NEWS.d/next/Library/2022-03-22-18-28-55.bpo-35540.nyijX9.rst new file mode 100644 index 00000000000000..b7aeee6c8c8f78 --- /dev/null +++ b/Misc/NEWS.d/next/Library/2022-03-22-18-28-55.bpo-35540.nyijX9.rst @@ -0,0 +1 @@ +Fix :func:`dataclasses.asdict` crash when :class:`collections.defaultdict` is present in the attributes.