Fixed @typechecked unable to find the code when PEP 695 type parameters are used

agronholm · agronholm · commit c5d91e91268b · 2025-03-06T01:25:55.000+02:00
Fixes #500.
diff --git a/docs/versionhistory.rst b/docs/versionhistory.rst
@@ -4,6 +4,12 @@ Version history
 This library adheres to
 `Semantic Versioning 2.0 <https://semver.org/#semantic-versioning-200>`_.
 
+**UNRELEASED**
+
+- Fixed ``@typechecked`` unable to find the target function or method if it or the
+  containing class had PEP 695 type parameters on them
+  (`#500 <https://github.com/agronholm/typeguard/issues/500>`_)
+
 **4.4.2** (2025-02-16)
 
 - Fixed ``TypeCheckError`` in unpacking assignment involving properties of a parameter
diff --git a/src/typeguard/_decorators.py b/src/typeguard/_decorators.py
@@ -36,18 +36,16 @@ def make_cell(value: object) -> _Cell:
 def find_target_function(
     new_code: CodeType, target_path: Sequence[str], firstlineno: int
 ) -> CodeType | None:
-    target_name = target_path[0]
     for const in new_code.co_consts:
         if isinstance(const, CodeType):
-            if const.co_name == target_name:
-                if const.co_firstlineno == firstlineno:
-                    return const
-                elif len(target_path) > 1:
-                    target_code = find_target_function(
-                        const, target_path[1:], firstlineno
-                    )
-                    if target_code:
-                        return target_code
+            new_path = (
+                target_path[1:] if const.co_name == target_path[0] else target_path
+            )
+            if not new_path and const.co_firstlineno == firstlineno:
+                return const
+
+            if target_code := find_target_function(const, new_path, firstlineno):
+                return target_code
 
     return None
 
diff --git a/tests/pep695.py b/tests/pep695.py
@@ -0,0 +1,12 @@
+from typeguard import typechecked
+
+
+@typechecked
+class ParametrizedClass[T]:
+    def method(self, x: T, y: str) -> T:
+        return x
+
+
+@typechecked
+def parametrized_func[T](x: T, y: str) -> T:
+    return x
diff --git a/tests/test_instrumentation.py b/tests/test_instrumentation.py
@@ -78,9 +78,18 @@ def dummymodule(method: str):
 def deferredannos(method: str):
     if sys.version_info < (3, 14):
         raise pytest.skip("Deferred annotations are only supported in Python 3.14+")
+
     return _fixture_module("deferredannos", method)
 
 
+@pytest.fixture(scope="module")
+def pep695(method: str):
+    if sys.version_info < (3, 12):
+        raise pytest.skip("PEP 695 type parameter syntax requires Python 3.12+")
+
+    return _fixture_module("pep695", method)
+
+
 def test_type_checked_func(dummymodule):
     assert dummymodule.type_checked_func(2, 3) == 6
 
@@ -386,3 +395,25 @@ def test_failure(self, deferredannos):
             match=r'argument "x" \(int\) is not an instance of deferredannos.NotYetDefined',
         ):
             deferredannos.uses_forwardref(1)
+
+
+class TestParametrized:
+    def test_success_func(self, pep695):
+        assert pep695.parametrized_func(1, "2") == 1
+
+    def test_success_method(self, pep695):
+        assert pep695.ParametrizedClass[int]().method(1, "2") == 1
+
+    def test_failure_func(self, pep695):
+        with pytest.raises(
+            TypeCheckError,
+            match=r'argument "y" \(int\) is not an instance of str',
+        ):
+            pep695.parametrized_func(1, 2)
+
+    def test_failure_method(self, pep695):
+        with pytest.raises(
+            TypeCheckError,
+            match=r'argument "y" \(int\) is not an instance of str',
+        ):
+            pep695.ParametrizedClass[int]().method("str", 2)
