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Backport type_params fix from CPython #646

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Merged
merged 1 commit into from
Aug 18, 2025
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Merged

Backport type_params fix from CPython #646

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3 changes: 2 additions & 1 deletion CHANGELOG.md
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Original file line number Diff line number Diff line change
Expand Up @@ -4,7 +4,8 @@
[`annotationlib.type_repr`](https://docs.python.org/3.14/library/annotationlib.html#annotationlib.type_repr),
introduced in Python 3.14 (CPython PR [#124551](https://github.com/python/cpython/pull/124551),
originally by Jelle Zijlstra). Patch by Semyon Moroz.

- Fix behavior of type params in `typing_extensions.evaluate_forward_ref`. Backport of
CPython PR [#137227](https://github.com/python/cpython/pull/137227) by Jelle Zijlstra.

# Release 4.14.1 (July 4, 2025)

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7 changes: 3 additions & 4 deletions src/test_typing_extensions.py
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Expand Up @@ -9194,10 +9194,9 @@ class Gen[Tx]:
not_Tx = TypeVar("Tx") # different TypeVar with same name
self.assertIs(evaluate_forward_ref(typing.ForwardRef("Tx"), type_params=(not_Tx,), owner=Gen), not_Tx)

# globals can take higher precedence
if _FORWARD_REF_HAS_CLASS:
self.assertIs(evaluate_forward_ref(typing.ForwardRef("Tx", is_class=True), owner=Gen, globals={"Tx": str}), str)
self.assertIs(evaluate_forward_ref(typing.ForwardRef("Tx", is_class=True), owner=Gen, type_params=(not_Tx,), globals={"Tx": str}), str)
# globals do not take higher precedence
self.assertIs(evaluate_forward_ref(typing.ForwardRef("Tx", is_class=True), owner=Gen, globals={"Tx": str}), Tx)
self.assertIs(evaluate_forward_ref(typing.ForwardRef("Tx", is_class=True), owner=Gen, type_params=(not_Tx,), globals={"Tx": str}), not_Tx)

with self.assertRaises(NameError):
evaluate_forward_ref(typing.ForwardRef("alias"), type_params=Gen.__type_params__)
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18 changes: 4 additions & 14 deletions src/typing_extensions.py
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Expand Up @@ -4065,23 +4065,13 @@ def _eval_with_owner(
# as a way of emulating annotation scopes when calling `eval()`
type_params = getattr(owner, "__type_params__", None)

# type parameters require some special handling,
# as they exist in their own scope
# but `eval()` does not have a dedicated parameter for that scope.
# For classes, names in type parameter scopes should override
# names in the global scope (which here are called `localns`!),
# but should in turn be overridden by names in the class scope
# (which here are called `globalns`!)
# Type parameters exist in their own scope, which is logically
# between the locals and the globals. We simulate this by adding
# them to the globals.
if type_params is not None:
globals = dict(globals)
locals = dict(locals)
for param in type_params:
param_name = param.__name__
if (
_FORWARD_REF_HAS_CLASS and not forward_ref.__forward_is_class__
) or param_name not in globals:
globals[param_name] = param
locals.pop(param_name, None)
globals[param.__name__] = param

arg = forward_ref.__forward_arg__
if arg.isidentifier() and not keyword.iskeyword(arg):
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