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gh-124176: create_autospec must not change how dataclass defaults are mocked #124724

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gh-124176: create_autospec must not change how dataclass defaults are mocked #124724

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gh-124176: `create_autospec` must not change how dataclass defaults a…
sobolevn Sep 28, 2024
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15 changes: 15 additions & 0 deletions Lib/test/test_unittest/testmock/testhelpers.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1107,6 +1107,21 @@ class WithNonFields:
with self.assertRaisesRegex(AttributeError, msg):
mock.b

def test_dataclass_with_wider_default(self):
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# If field defines an actual default, we don't need to change
# the default type. Since this is how it used to work before #124176
@dataclass
class WithWiderDefault:
narrow_default: int | None = field(default=30)

for mock in [
create_autospec(WithWiderDefault, instance=True),
create_autospec(WithWiderDefault()),
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]:
with self.subTest(mock=mock):
self.assertIs(mock.narrow_default.__class__, int)


class TestCallList(unittest.TestCase):

def test_args_list_contains_call_list(self):
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8 changes: 5 additions & 3 deletions Lib/unittest/mock.py
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Expand Up @@ -2758,13 +2758,15 @@ def create_autospec(spec, spec_set=False, instance=False, _parent=None,
f'[object={spec!r}]')
is_async_func = _is_async_func(spec)

entries = [(entry, _missing) for entry in dir(spec)]
base_entries = {entry: _missing for entry in dir(spec)}
if is_type and instance and is_dataclass(spec):
dataclass_fields = fields(spec)
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entries.extend((f.name, f.type) for f in dataclass_fields)
entries = {f.name: f.type for f in dataclass_fields}
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How come we don't end up using UnionType here from the int | None annotation?

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@sobolevn sobolevn Sep 30, 2024 •
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Because I override entries with default_entries here: https://github.com/python/cpython/pull/124724/files#diff-347d0254250a1ab7ab8e31b405e2c35b74cd2838df4ee74f1b658a459eb91f1aR2765

This way field(default=0) has the priority over the annotation.

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Two questions from that:

  1. What happens with a class such as this?

    @dataclass
class SampleClass:
    sample_attr: int | None

  2. What does the mock machinery do with the field object it gets in the case you show above?

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  1. In this case spec would be UnionType, because we have no default
  2. Mock does nothing special to field, dataclass itself sets SampleClass.sample_attr = default, and we just use getattr to get the existing default

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Would it be possible to add a unit test (or more if necessary) showing this?

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Done!

entries.update(base_entries)
_kwargs = {'spec': [f.name for f in dataclass_fields]}
else:
_kwargs = {'spec': spec}
entries = base_entries

if spec_set:
_kwargs = {'spec_set': spec}
Expand Down Expand Up @@ -2822,7 +2824,7 @@ def create_autospec(spec, spec_set=False, instance=False, _parent=None,
_name='()', _parent=mock,
wraps=wrapped)

for entry, original in entries:
for entry, original in entries.items():
if _is_magic(entry):
# MagicMock already does the useful magic methods for us
continue
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