gh-156924: Try reifying lazy imports in `ForwarRef.evaluate()` by Viicos · Pull Request #156940 · python/cpython · GitHub
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gh-156924: Try reifying lazy imports in ForwarRef.evaluate() #156940

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Merged
JelleZijlstra merged 4 commits into from
Sep 9, 2026
+136 −3
Merged

gh-156924: Try reifying lazy imports in ForwarRef.evaluate() #156940

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8754d32
gh-156924: Try reifying lazy imports in `ForwarRef.evaluate()`
Viicos Sep 4, 2026
a490405
Update Lib/annotationlib.py
Viicos Sep 4, 2026
7e4ffa8
Add extra test
Viicos Sep 7, 2026
51cdab4
Link LazyImportType in NEWS
encukou Sep 9, 2026
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21 changes: 18 additions & 3 deletions Lib/annotationlib.py
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112 changes: 112 additions & 0 deletions Lib/test/test_annotationlib.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2179,6 +2179,118 @@ def test_evaluate_forwardref_format(self):
support.EqualToForwardRef('"a" + 1'),
)

def test_evaluate_lazy_import(self):
ns = {}
exec(
textwrap.dedent(
"""
lazy from test.test_lazy_import.data.basic2 import x
lazy from test.test_lazy_import.data.broken_module import y

class A:
a: x

class B:
b: y
"""
),
ns,
)
self.addCleanup(
import_helper.unload, "test.test_lazy_import.data.basic2"
)
self.addCleanup(
import_helper.unload, "test.test_lazy_import.data.broken_module"
)
self.assertIs(type(ns["x"]), types.LazyImportType)
self.assertIs(type(ns["y"]), types.LazyImportType)

# The lazy import resolves successfully:
for format in (Format.VALUE, Format.FORWARDREF):
with self.subTest(format=format):
self.assertEqual(
ForwardRef("x").evaluate(globals=ns, format=format), 42
)
self.assertEqual(
ForwardRef("x").evaluate(locals=ns, format=format), 42
)
self.assertEqual(
get_annotations(ns["A"], format=Format.FORWARDREF), {"a": 42}
)

# The lazy import fails to resolve:
fr = ForwardRef("y")
with self.assertRaisesRegex(ValueError, "always fails to import"):
fr.evaluate(globals=ns, format=Format.VALUE)
with self.assertRaisesRegex(ValueError, "always fails to import"):
fr.evaluate(locals=ns, format=Format.VALUE)
self.assertIs(fr.evaluate(globals=ns, format=Format.FORWARDREF), fr)
self.assertIs(fr.evaluate(locals=ns, format=Format.FORWARDREF), fr)

annos = get_annotations(ns["B"], format=Format.FORWARDREF)
self.assertEqual(
annos,
{"b": support.EqualToForwardRef("y", is_class=True, owner=ns["B"])},
)
with self.assertRaisesRegex(ValueError, "always fails to import"):
annos["b"].evaluate(format=Format.VALUE)
with self.assertRaisesRegex(ValueError, "always fails to import"):
get_annotations(ns["B"], format=Format.VALUE)

def test_get_annotations_lazy_import(self):
ns = {}
exec(
textwrap.dedent(
"""
lazy from test.test_lazy_import.data.basic2 import x
lazy from test.test_lazy_import.data.broken_module import y

class A:
a: object.fail
b: x

class B:
a: object.fail
b: y
"""
),
ns,
)
self.addCleanup(
import_helper.unload, "test.test_lazy_import.data.basic2"
)
self.addCleanup(
import_helper.unload, "test.test_lazy_import.data.broken_module"
)
self.assertIs(type(ns["x"]), types.LazyImportType)
self.assertIs(type(ns["y"]), types.LazyImportType)

annos = get_annotations(ns["A"], format=Format.FORWARDREF)
self.assertEqual(
annos,
{
"a": support.EqualToForwardRef(
"object.fail", is_class=True, owner=ns["A"]
),
"b": 42,
},
)

annos = get_annotations(ns["B"], format=Format.FORWARDREF)
self.assertEqual(
annos,
{
"a": support.EqualToForwardRef(
"object.fail", is_class=True, owner=ns["B"]
),
"b": support.EqualToForwardRef(
"y", is_class=True, owner=ns["B"]
),
},
)
with self.assertRaisesRegex(ValueError, "always fails to import"):
annos["b"].evaluate(format=Format.VALUE)

def test_evaluate_notimplemented_format(self):
class C:
x: alias
Expand Down
6 changes: 6 additions & 0 deletions Misc/NEWS.d/next/Library/2026-09-04-14-15-31.gh-issue-156924.3Ux7IJ.rst
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