gh-82062: correctly set module for built-in instance methods in inspect.signature()

Lib/inspect.py

@@ -2285,9 +2285,12 @@ def _signature_fromstr(cls, obj, s, skip_bound_arg=True):
 
     module = None
     module_dict = {}
-    module_name = (getattr(obj, '__module__', None) or
-                   getattr(getattr(obj, '__objclass__', None),
-                           '__module__', None))
+
+    module_name = getattr(obj, '__module__', None)
+    if not module_name:
+        objclass = getattr(obj, '__objclass__', None)
+        module_name = getattr(objclass, '__module__', None)
+
     if module_name:
         module = sys.modules.get(module_name, None)
         if module:

Lib/test/test_capi/test_misc.py

@@ -6,7 +6,6 @@
 import contextlib
 import importlib.machinery
 import importlib.util
-import inspect
 import json
 import os
 import pickle
@@ -184,12 +183,6 @@ def test_docstring_signature_parsing(self):
         self.assertEqual(_testcapi.docstring_with_signature_and_extra_newlines.__text_signature__,
             "($module, /, parameter)")
 
-    @unittest.skipIf(MISSING_C_DOCSTRINGS,
-                     "Signature information for builtins requires docstrings")
-    def test_signature_parsing_with_defaults(self):
-        meth = _testcapi.DocStringUnrepresentableSignatureTest.with_default
-        self.assertEqual(str(inspect.signature(meth)), '(self, /, x=1)')
-
     def test_c_type_with_matrix_multiplication(self):
         M = _testcapi.matmulType
         m1 = M()

Lib/test/test_inspect/test_inspect.py

@@ -3069,6 +3069,13 @@ def test_signature_on_builtins_no_signature(self):
                 self.assertEqual(inspect.signature(builtin),
                                  inspect.signature(template))
 
+    @unittest.skipIf(MISSING_C_DOCSTRINGS,
+                     "Signature information for builtins requires docstrings")
+    def test_signature_parsing_with_defaults(self):
+        _testcapi = import_helper.import_module("_testcapi")
+        meth = _testcapi.DocStringUnrepresentableSignatureTest.with_default
+        self.assertEqual(str(inspect.signature(meth)), '(self, /, x=1)')
+
     def test_signature_on_non_function(self):
         with self.assertRaisesRegex(TypeError, 'is not a callable object'):
             inspect.signature(42)

Misc/NEWS.d/next/Library/2024-02-11-07-31-43.gh-issue-82062.eeS6w7.rst

@@ -1,2 +1,3 @@
-Fix :func:`inspect.signature()` to correctly set extension module for
-built-in instance methods.
+Fix :func:`inspect.signature()` to correctly set extension module for built-in
+instance methods.  They lacks ``__module__`` attribute, so we use instead
+``__objclass__.__module__`` attribute.