Fixed TypeCheckError in unpacking assignment involving properties

agronholm · agronholm · commit f282802f7f1e · 2025-01-19T22:01:18.000+02:00
Fixes #506.
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 ``TypeCheckError`` in unpacking assignment involving properties of a parameter
+  of the function (`#506 <https://github.com/agronholm/typeguard/issues/506>`_;
+  regression introduced in v4.4.1)
+
 **4.4.1** (2024-11-03)
 
 - Dropped Python 3.8 support
diff --git a/src/typeguard/_transformer.py b/src/typeguard/_transformer.py
@@ -1073,8 +1073,9 @@ def visit_Assign(self, node: Assign) -> Any:
 
                         path.insert(0, exp.id)
                         name = prefix + ".".join(path)
-                        annotation = self._memo.variable_annotations.get(exp.id)
-                        if annotation:
+                        if len(path) == 1 and (
+                            annotation := self._memo.variable_annotations.get(exp.id)
+                        ):
                             annotations_.append((Constant(name), annotation))
                             check_required = True
                         else:
diff --git a/tests/dummymodule.py b/tests/dummymodule.py
@@ -74,6 +74,9 @@ class Metaclass(type):
 
 @typechecked
 class DummyClass(metaclass=Metaclass):
+    bar: str
+    baz: int
+
     def type_checked_method(self, x: int, y: int) -> int:
         return x * y
 
@@ -270,6 +273,11 @@ def unpacking_assign_star_no_annotation(value: Any) -> Tuple[int, List[bytes], s
     return x, y, z
 
 
+@typechecked
+def attribute_assign_unpacking(obj: DummyClass) -> None:
+    obj.bar, obj.baz = "foo", 123123
+
+
 @typechecked(forward_ref_policy=ForwardRefPolicy.ERROR)
 def override_forward_ref_policy(value: "NonexistentType") -> None:  # noqa: F821
     pass
diff --git a/tests/test_instrumentation.py b/tests/test_instrumentation.py
@@ -250,6 +250,11 @@ def test_unpacking_assign_star_no_annotation_success(dummymodule):
     )
 
 
+def test_attribute_assign_unpacking(dummymodule):
+    foo = dummymodule.DummyClass()
+    dummymodule.attribute_assign_unpacking(foo)
+
+
 def test_unpacking_assign_star_no_annotation_fail(dummymodule):
     with pytest.raises(
         TypeCheckError, match=r"value assigned to z \(bytes\) is not an instance of str"
