https://github.com/python/cpython/commit/402668b2b1a63a2b3cfd7a2ede07f6786f9beb8e commit: 402668b2b1a63a2b3cfd7a2ede07f6786f9beb8e branch: main author: Aniket <[email protected]> committer: vstinner <[email protected]> date: 2026-06-11T17:15:29Z summary:
gh-138991: Update dataclass documentation for new eq behavior in Python 3.13 (#139007) And add tests. Co-authored-by: Victor Stinner <[email protected]> files: M Doc/library/dataclasses.rst M Lib/test/test_dataclasses/__init__.py diff --git a/Doc/library/dataclasses.rst b/Doc/library/dataclasses.rst index 954edc4506df1a3..ce59d89843e761d 100644 --- a/Doc/library/dataclasses.rst +++ b/Doc/library/dataclasses.rst @@ -100,12 +100,25 @@ Module contents ignored. - *eq*: If true (the default), an :meth:`~object.__eq__` method will be - generated. This method compares the class as if it were a tuple - of its fields, in order. Both instances in the comparison must - be of the identical type. + generated. - If the class already defines :meth:`!__eq__`, this parameter is - ignored. + This method compares the class by comparing each field in order. Both + instances in the comparison must be of the identical type. + + If the class already defines :meth:`!__eq__`, this parameter is ignored. + + .. versionchanged:: 3.13 + The generated ``__eq__`` method now compares each field individually + (for example, ``self.a == other.a and self.b == other.b``), rather than + comparing tuples of fields as in previous versions. + + This change makes the comparison faster but it may alter results in cases + where attributes compare equal by identity but not by value (such as + ``float('nan')``). + + In Python 3.12 and earlier, the comparison was performed by creating + tuples of the fields and comparing them (for example, + ``(self.a, self.b) == (other.a, other.b)``). - *order*: If true (the default is ``False``), :meth:`~object.__lt__`, :meth:`~object.__le__`, :meth:`~object.__gt__`, and :meth:`~object.__ge__` methods will be diff --git a/Lib/test/test_dataclasses/__init__.py b/Lib/test/test_dataclasses/__init__.py index 2468e3e64dd621c..423247c92ce3c29 100644 --- a/Lib/test/test_dataclasses/__init__.py +++ b/Lib/test/test_dataclasses/__init__.py @@ -2792,6 +2792,55 @@ def __eq__(self, other): self.assertEqual(C(1), 5) self.assertNotEqual(C(1), 1) + def test_eq_field_by_field(self): + @dataclasses.dataclass + class Point: + x: int + y: int + + p1 = Point(1, 2) + p2 = Point(1, 2) + p3 = Point(2, 1) + self.assertEqual(p1, p2) + self.assertNotEqual(p1, p3) + + def test_eq_type_check(self): + @dataclasses.dataclass + class A: + x: int + + @dataclasses.dataclass + class B: + x: int + + a = A(1) + b = B(1) + self.assertNotEqual(a, b) + + def test_eq_custom_field(self): + class AlwaysEqual(int): + def __eq__(self, other): + return True + + @dataclasses.dataclass + class Foo: + x: AlwaysEqual + y: int + + f1 = Foo(AlwaysEqual(1), 2) + f2 = Foo(AlwaysEqual(2), 2) + self.assertEqual(f1, f2) + + def test_eq_nan_field(self): + @dataclasses.dataclass + class D: + x: float + + nan = float('nan') + d1 = D(nan) + d2 = D(nan) + self.assertNotEqual(d1, d2) + class TestOrdering(unittest.TestCase): def test_functools_total_ordering(self): _______________________________________________ Python-checkins mailing list -- [email protected] To unsubscribe send an email to [email protected] https://mail.python.org/mailman3//lists/python-checkins.python.org Member address: [email protected]
