From aca77b5530c34fb2ada0fe02fb83f4c9fa9256f3 Mon Sep 17 00:00:00 2001
From: Tian Gao <gaogaotiantian@hotmail.com>
Date: Sun, 4 Jun 2023 14:26:01 -0700
Subject: [PATCH] =?utf8?q?[3.11]=20gh-105080:=20Fixed=20inconsistent=20sig?=
 =?utf8?q?nature=20on=20derived=20classes=20(GH=E2=80=A6=20(#105274)?=
MIME-Version: 1.0
Content-Type: text/plain; charset=utf8
Content-Transfer-Encoding: 8bit

---
 Lib/inspect.py                                | 23 ++++++++++---------
 Lib/test/test_inspect.py                      | 18 +++++++++++++++
 ...-06-02-02-38-26.gh-issue-105080.2imGMg.rst |  1 +
 3 files changed, 31 insertions(+), 11 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Library/2023-06-02-02-38-26.gh-issue-105080.2imGMg.rst

diff --git a/Lib/inspect.py b/Lib/inspect.py
index 14569a510a05..655b04b0eed4 100644
--- a/Lib/inspect.py
+++ b/Lib/inspect.py
@@ -2538,17 +2538,18 @@ def _signature_from_callable(obj, *,
             factory_method = None
             new = _signature_get_user_defined_method(obj, '__new__')
             init = _signature_get_user_defined_method(obj, '__init__')
-            # Now we check if the 'obj' class has an own '__new__' method
-            if '__new__' in obj.__dict__:
-                factory_method = new
-            # or an own '__init__' method
-            elif '__init__' in obj.__dict__:
-                factory_method = init
-            # If not, we take inherited '__new__' or '__init__', if present
-            elif new is not None:
-                factory_method = new
-            elif init is not None:
-                factory_method = init
+
+            # Go through the MRO and see if any class has user-defined
+            # pure Python __new__ or __init__ method
+            for base in obj.__mro__:
+                # Now we check if the 'obj' class has an own '__new__' method
+                if new is not None and '__new__' in base.__dict__:
+                    factory_method = new
+                    break
+                # or an own '__init__' method
+                elif init is not None and '__init__' in base.__dict__:
+                    factory_method = init
+                    break
 
             if factory_method is not None:
                 sig = _get_signature_of(factory_method)
diff --git a/Lib/test/test_inspect.py b/Lib/test/test_inspect.py
index 2783f7f8a08e..fb4cba057210 100644
--- a/Lib/test/test_inspect.py
+++ b/Lib/test/test_inspect.py
@@ -3688,6 +3688,24 @@ class TestSignatureObject(unittest.TestCase):
                 self.assertEqual(signature_func(foo), inspect.Signature())
         self.assertEqual(inspect.get_annotations(foo), {})
 
+    def test_signature_on_derived_classes(self):
+        # gh-105080: Make sure that signatures are consistent on derived classes
+
+        class B:
+            def __new__(self, *args, **kwargs):
+                return super().__new__(self)
+            def __init__(self, value):
+                self.value = value
+
+        class D1(B):
+            def __init__(self, value):
+                super().__init__(value)
+
+        class D2(D1):
+            pass
+
+        self.assertEqual(inspect.signature(D2), inspect.signature(D1))
+
 
 class TestParameterObject(unittest.TestCase):
     def test_signature_parameter_kinds(self):
diff --git a/Misc/NEWS.d/next/Library/2023-06-02-02-38-26.gh-issue-105080.2imGMg.rst b/Misc/NEWS.d/next/Library/2023-06-02-02-38-26.gh-issue-105080.2imGMg.rst
new file mode 100644
index 000000000000..efe8365a7644
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2023-06-02-02-38-26.gh-issue-105080.2imGMg.rst
@@ -0,0 +1 @@
+Fixed inconsistent signature on derived classes for :func:`inspect.signature`
-- 
2.47.3