diff --git a/Lib/dataclasses.py b/Lib/dataclasses.py index aca60501d0e..8643589077a 100644 --- a/Lib/dataclasses.py +++ b/Lib/dataclasses.py @@ -447,7 +447,7 @@ def _field_assign(frozen, name, value, self_name): return f'{self_name}.{name}={value}' -def _field_init(f, frozen, globals, self_name): +def _field_init(f, frozen, globals, self_name, slots): # Return the text of the line in the body of __init__ that will # initialize this field. @@ -487,9 +487,15 @@ def _field_init(f, frozen, globals, self_name): globals[default_name] = f.default value = f.name else: - # This field does not need initialization. Signify that - # to the caller by returning None. - return None + # If the class has slots, then initialize this field. + if slots and f.default is not MISSING: + globals[default_name] = f.default + value = default_name + else: + # This field does not need initialization: reading from it will + # just use the class attribute that contains the default. + # Signify that to the caller by returning None. + return None # Only test this now, so that we can create variables for the # default. However, return None to signify that we're not going @@ -521,7 +527,7 @@ def _init_param(f): def _init_fn(fields, std_fields, kw_only_fields, frozen, has_post_init, - self_name, globals): + self_name, globals, slots): # fields contains both real fields and InitVar pseudo-fields. # Make sure we don't have fields without defaults following fields @@ -548,7 +554,7 @@ def _init_fn(fields, std_fields, kw_only_fields, frozen, has_post_init, body_lines = [] for f in fields: - line = _field_init(f, frozen, locals, self_name) + line = _field_init(f, frozen, locals, self_name, slots) # line is None means that this field doesn't require # initialization (it's a pseudo-field). Just skip it. if line: @@ -1027,6 +1033,7 @@ def _process_class(cls, init, repr, eq, order, unsafe_hash, frozen, '__dataclass_self__' if 'self' in fields else 'self', globals, + slots, )) # Get the fields as a list, and include only real fields. This is diff --git a/Lib/test/test_dataclasses.py b/Lib/test/test_dataclasses.py index b00d0484d38..bcd004f4ec3 100644 --- a/Lib/test/test_dataclasses.py +++ b/Lib/test/test_dataclasses.py @@ -2880,6 +2880,28 @@ class TestSlots(unittest.TestCase): self.assertIsNot(obj, p) self.assertEqual(obj, p) + def test_slots_with_default_no_init(self): + # Originally reported in bpo-44649. + @dataclass(slots=True) + class A: + a: str + b: str = field(default='b', init=False) + + obj = A("a") + self.assertEqual(obj.a, 'a') + self.assertEqual(obj.b, 'b') + + def test_slots_with_default_factory_no_init(self): + # Originally reported in bpo-44649. + @dataclass(slots=True) + class A: + a: str + b: str = field(default_factory=lambda:'b', init=False) + + obj = A("a") + self.assertEqual(obj.a, 'a') + self.assertEqual(obj.b, 'b') + class TestDescriptors(unittest.TestCase): def test_set_name(self): # See bpo-33141. diff --git a/Misc/NEWS.d/next/Library/2021-11-21-20-50-42.bpo-44649.E8M936.rst b/Misc/NEWS.d/next/Library/2021-11-21-20-50-42.bpo-44649.E8M936.rst new file mode 100644 index 00000000000..f6391a915a8 --- /dev/null +++ b/Misc/NEWS.d/next/Library/2021-11-21-20-50-42.bpo-44649.E8M936.rst @@ -0,0 +1,2 @@ +Handle dataclass(slots=True) with a field that has default a default value, +but for which init=False.