Mangle __parameters in __annotations__ dict properly. Issue #20625.

1 files changed, 16 insertions, 0 deletions

diff --git a/Lib/test/test_inspect.py b/Lib/test/test_inspect.py
index 3f204191bf..a34a418cca 100644
--- a/Lib/test/test_inspect.py
+++ b/Lib/test/test_inspect.py
@@ -2390,6 +2390,22 @@ class TestSignatureObject(unittest.TestCase):
         self.assertEqual(sig.return_annotation, 42)
         self.assertEqual(sig, inspect.signature(test))
 
+    def test_signature_on_mangled_parameters(self):
+        class Spam:
+            def foo(self, __p1:1=2, *, __p2:2=3):
+                pass
+        class Ham(Spam):
+            pass
+
+        self.assertEqual(self.signature(Spam.foo),
+                         ((('self', ..., ..., "positional_or_keyword"),
+                           ('_Spam__p1', 2, 1, "positional_or_keyword"),
+                           ('_Spam__p2', 3, 2, "keyword_only")),
+                          ...))
+
+        self.assertEqual(self.signature(Spam.foo),
+                         self.signature(Ham.foo))
+
 
 class TestParameterObject(unittest.TestCase):
     def test_signature_parameter_kinds(self):