Fix a crash in pytype/overriding_checks.py.

Very rarely, the type of a kwargs parameter can be a plain dict rather than a
Dict[str, X].

PiperOrigin-RevId: 445439268

Author: rchen152

pytype/overriding_checks.py

@@ -273,11 +273,14 @@ def _check_keyword_only_parameters(method_signature, base_signature,
       continue
 
     if method_param_name == method_signature.kwargs_name:
-      # If kwargs are annotated with type T in the function definition,
-      # the annotation in the signature will be Dict[str, T].
-      assert isinstance(method_param_type, abstract.ParameterizedClass)
-      method_param_type = method_param_type.get_formal_type_parameter(
-          abstract_utils.V)
+      if isinstance(method_param_type, abstract.ParameterizedClass):
+        # If kwargs are annotated with type T in the function definition,
+        # the annotation in the signature will be Dict[str, T].
+        method_param_type = method_param_type.get_formal_type_parameter(
+            abstract_utils.V)
+      else:
+        # If the kwargs type is a plain dict, there's nothing to check.
+        continue
 
     # Parameter type of the overridden method must be a subtype of the
     # parameter type of the overriding method.

pytype/tests/test_overriding.py

@@ -4,7 +4,7 @@
 from pytype.tests import test_utils
 
 
-class OverrdingTest(test_base.BaseTest):
+class OverridingTest(test_base.BaseTest):
   """Tests for overridden and overriding methods signature match."""
 
   # Positional-or-keyword -> positional-or-keyword, same name or underscore.
@@ -779,6 +779,16 @@ def f(self, a: int, /) -> None:  # signature-mismatch
           pass
     """)
 
+  def test_callable_multiple_inheritance(self):
+    self.Check("""
+      from typing import Callable
+      class Foo:
+        def __call__(self, x: int, *, y: str):
+          pass
+      class Bar(Callable, Foo):
+        pass
+    """)
+
 
 if __name__ == "__main__":
   test_base.main()