Pass signature check if inspect.signature throws a ValueError

overrides/signature.py

@@ -85,7 +85,12 @@ def ensure_signature_is_compatible(
     """
     super_callable = _unbound_func(super_callable)
     sub_callable = _unbound_func(sub_callable)
-    super_sig = inspect.signature(super_callable)
+
+    try:
+        super_sig = inspect.signature(super_callable)
+    except ValueError:
+        return
+
     super_type_hints = _get_type_hints(super_callable)
     sub_sig = inspect.signature(sub_callable)
     sub_type_hints = _get_type_hints(sub_callable)

tests/test_overrides.py

@@ -1,4 +1,6 @@
+import sys
 import unittest
+from contextlib import contextmanager
 from typing import Generic, TypeVar
 
 import test_somepackage
@@ -7,6 +9,11 @@
 TObject = TypeVar("TObject", bound="Foo")
 
 
+@contextmanager
+def no_error():
+    yield
+
+
 class SubClassOfGeneric(Generic[TObject]):
     def some_method(self):
         """Generic sub class."""
@@ -61,10 +68,6 @@ class SubclassOfInt(int):
     def __str__(self):
         return "subclass of int"
 
-    @overrides
-    def bit_length(self):
-        pass
-
 
 class CheckAtRuntime(SuperClass):
     @overrides(check_at_runtime=True)
@@ -146,6 +149,29 @@ def test_overrides_check_at_runtime(self):
         with self.assertRaises(TypeError):
             CheckAtRuntime().some_method(1)
 
+    def test_overrides_builtin_method_correct_signature(self):
+        class SubclassOfInt(int):
+            @overrides
+            def bit_length(self):
+                return super().bit_length()
+
+        x = SubclassOfInt(1)
+        self.assertEqual(x.bit_length(), 1)
+
+    def test_overrides_builtin_method_incorrect_signature(self):
+        if sys.version_info >= (3, 7):
+            expected_error = self.assertRaises(TypeError)
+        else:
+            # In 3.6 inspecting signature's isn't possible for builtin
+            # methods so this this passes the signature check.
+            expected_error = no_error()
+
+        with expected_error:
+            class SubclassOfInt(int):
+                @overrides
+                def bit_length(self, _):
+                    "This will fail, bit_length takes in no arguments"
+
 
 if __name__ == "__main__":
     unittest.main()