bpo-45663: Fix is_dataclass() for dataclasses which are subclasses of… · python/cpython@1905071 (original) (raw)

3 files changed

lines changed

Original file line number Diff line number Diff line change
@@ -1047,7 +1047,7 @@ def _is_dataclass_instance(obj):
1047 1047 def is_dataclass(obj):
1048 1048 """Returns True if obj is a dataclass or an instance of a
1049 1049 dataclass."""
1050 -cls = obj if isinstance(obj, type) else type(obj)
1050 +cls = obj if isinstance(obj, type) and not isinstance(obj, GenericAlias) else type(obj)
1051 1051 return hasattr(cls, _FIELDS)
1052 1052
1053 1053
Original file line number Diff line number Diff line change
@@ -7,6 +7,7 @@
7 7 import pickle
8 8 import inspect
9 9 import builtins
10 +import types
10 11 import unittest
11 12 from unittest.mock import Mock
12 13 from typing import ClassVar, Any, List, Union, Tuple, Dict, Generic, TypeVar, Optional, Protocol
@@ -1348,6 +1349,17 @@ class B:
1348 1349 with self.assertRaisesRegex(TypeError, 'should be called on dataclass instances'):
1349 1350 replace(obj, x=0)
1350 1351
1352 +def test_is_dataclass_genericalias(self):
1353 +@dataclass
1354 +class A(types.GenericAlias):
1355 +origin: type
1356 +args: type
1357 +self.assertTrue(is_dataclass(A))
1358 +a = A(list, int)
1359 +self.assertTrue(is_dataclass(type(a)))
1360 +self.assertTrue(is_dataclass(a))
1361 +
1362 +
1351 1363 def test_helper_fields_with_class_instance(self):
1352 1364 # Check that we can call fields() on either a class or instance,
1353 1365 # and get back the same thing.
Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
1 +Fix :func:`dataclasses.is_dataclass` for dataclasses which are subclasses of
2 +:class:`types.GenericAlias`.