10000 gh-119180: Make FORWARDREF format look at __annotations__ first by JelleZijlstra · Pull Request #124479 · python/cpython · GitHub
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gh-119180: Make FORWARDREF format look at __annotations__ first #124479

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Merged
merged 1 commit into from
Sep 25, 2024
Merged

gh-119180: Make FORWARDREF format look at __annotations__ first #124479

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81 changes: 59 additions & 22 deletions Lib/annotationlib.py
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Original file line number Diff line number Diff line change
Expand Up @@ -639,28 +639,38 @@ def get_annotations(
if eval_str and format != Format.VALUE:
raise ValueError("eval_str=True is only supported with format=Format.VALUE")

# For VALUE format, we look at __annotations__ directly.
if format != Format.VALUE:
annotate = get_annotate_function(obj)
if annotate is not None:
ann = call_annotate_function(annotate, format, owner=obj)
if not isinstance(ann, dict):
raise ValueError(f"{obj!r}.__annotate__ returned a non-dict")
return dict(ann)

if isinstance(obj, type):
try:
ann = _BASE_GET_ANNOTATIONS(obj)
except AttributeError:
# For static types, the descriptor raises AttributeError.
return {}
else:
ann = getattr(obj, "__annotations__", None)
if ann is None:
return {}

if not isinstance(ann, dict):
raise ValueError(f"{obj!r}.__annotations__ is neither a dict nor None")
match format:
case Format.VALUE:
# For VALUE, we only look at __annotations__
ann = _get_dunder_annotations(obj)
case Format.FORWARDREF:
# For FORWARDREF, we use __annotations__ if it exists
try:
ann = _get_dunder_annotations(obj)
except NameError:
pass
else:
return dict(ann)

# But if __annotations__ threw a NameError, we try calling __annotate__
ann = _get_and_call_annotate(obj, format)
if ann is not None:
return ann

# If that didn't work either, we have a very weird object: evaluating
# __annotations__ threw NameError and there is no __annotate__. In that case,
# we fall back to trying __annotations__ again.
return dict(_get_dunder_annotations(obj))
case Format.SOURCE:
# For SOURCE, we try to call __annotate__
ann = _get_and_call_annotate(obj, format)
if ann is not None:
return ann
# But if we didn't get it, we use __annotations__ instead.
ann = _get_dunder_annotations(obj)
Comment on lines +669 to +670
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Is this right? If we can't get stringified annotations, I would think we'd want to return an empty dict, not fall back to returning non-stringified annotations. (Unless maybe __future__.annotations is active, in which case __annotations__ will be stringified anyway.)

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I just posted #124551 which instead stringifies the annotations we find.

return ann
case _:
raise ValueError(f"Unsupported format {format!r}")

if not ann:
return {}
Expand Down Expand Up @@ -725,3 +735,30 @@ def get_annotations(
for key, value in ann.items()
}
return return_value


def _get_and_call_annotate(obj, format):
annotate = get_annotate_function(obj)
if annotate is not None:
ann = call_annotate_function(annotate, format, owner=obj)
if not isinstance(ann, dict):
raise ValueError(f"{obj!r}.__annotate__ returned a non-dict")
return dict(ann)
return None


def _get_dunder_annotations(obj):
if isinstance(obj, type):
try:
ann = _BASE_GET_ANNOTATIONS(obj)
except AttributeError:
# For static types, the descriptor raises AttributeError.
return {}
else:
ann = getattr(obj, "__annotations__", None)
if ann is None:
return {}

if not isinstance(ann, dict):
raise ValueError(f"{obj!r}.__annotations__ is neither a dict nor None")
return dict(ann)
88 changes: 84 additions & 4 deletions Lib/test/test_annotationlib.py
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Original file line number Diff line number Diff line change
Expand Up @@ -705,17 +705,97 @@ def f(x: int):

self.assertEqual(annotationlib.get_annotations(f), {"x": int})
self.assertEqual(
annotationlib.get_annotations(f, format=annotationlib.Format.FORWARDREF),
annotationlib.get_annotations(f, format=Format.FORWARDREF),
{"x": int},
)

f.__annotations__["x"] = str
# The modification is reflected in VALUE (the default)
self.assertEqual(annotationlib.get_annotations(f), {"x": str})
# ... but not in FORWARDREF, which uses __annotate__
# ... and also in FORWARDREF, which tries __annotations__ if available
self.assertEqual(
annotationlib.get_annotations(f, format=annotationlib.Format.FORWARDREF),
{"x": int},
annotationlib.get_annotations(f, format=Format.FORWARDREF),
{"x": str},
)
# ... but not in SOURCE which always uses __annotate__
self.assertEqual(
annotationlib.get_annotations(f, format=Format.SOURCE),
{"x": "int"},
)

def test_non_dict_annotations(self):
class WeirdAnnotations:
@property
def __annotations__(self):
return "not a dict"

wa = WeirdAnnotations()
for format in Format:
with (
self.subTest(format=format),
self.assertRaisesRegex(
ValueError, r".*__annotations__ is neither a dict nor None"
),
):
annotationlib.get_annotations(wa, format=format)

def test_annotations_on_custom_object(self):
class HasAnnotations:
@property
def __annotations__(self):
return {"x": int}

ha = HasAnnotations()
self.assertEqual(
annotationlib.get_annotations(ha, format=Format.VALUE), {"x": int}
)
self.assertEqual(
annotationlib.get_annotations(ha, format=Format.FORWARDREF), {"x": int}
)

# TODO(gh-124412): This should return {'x': 'int'} instead.
self.assertEqual(
annotationlib.get_annotations(ha, format=Format.SOURCE), {"x": int}
)

def test_raising_annotations_on_custom_object(self):
class HasRaisingAnnotations:
@property
def __annotations__(self):
return {"x": undefined}

hra = HasRaisingAnnotations()

with self.assertRaises(NameError):
annotationlib.get_annotations(hra, format=Format.VALUE)

with self.assertRaises(NameError):
annotationlib.get_annotations(hra, format=Format.FORWARDREF)

undefined = float
self.assertEqual(
annotationlib.get_annotations(hra, format=Format.VALUE), {"x": float}
)

def test_forwardref_prefers_annotations(self):
class HasBoth:
@property
def __annotations__(self):
return {"x": int}

@property
def __annotate__(self):
return lambda format: {"x": str}

hb = HasBoth()
self.assertEqual(
annotationlib.get_annotations(hb, format=Format.VALUE), {"x": int}
)
self.assertEqual(
annotationlib.get_annotations(hb, format=Format.FORWARDREF), {"x": int}
)
self.assertEqual(
annotationlib.get_annotations(hb, format=Format.SOURCE), {"x": str}
)

def test_pep695_generic_class_with_future_annotations(self):
Expand Down
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