gh-131628: use duck-typing in inspect to support Cython

Lib/inspect.py

@@ -862,9 +862,9 @@ def getfile(object):
             if object.__module__ == '__main__':
                 raise OSError('source code not available')
         raise TypeError('{!r} is a built-in class'.format(object))
-    if ismethod(object):
+    if hasattr(object, '__func__'):
         object = object.__func__
-    if isfunction(object):
+    if hasattr(object, '__code__'):
         object = object.__code__
     if istraceback(object):
         object = object.tb_frame
@@ -1022,9 +1022,9 @@ def findsource(object):
             raise OSError('lineno is out of bounds')
         return lines, lnum
 
-    if ismethod(object):
+    if hasattr(object, '__func__'):
         object = object.__func__
-    if isfunction(object):
+    if hasattr(object, '__code__'):
         object = object.__code__
     if istraceback(object):
         object = object.tb_frame

Lib/test/test_inspect/inspect_fodder2.py

@@ -400,4 +400,34 @@ def func394():
 def func400():
     return 401
 
+# line 403
+class FunctionLike:
+    # Like a function compiled by Cython: it provides __code__, but it is not
+    # an instance of types.FunctionType.  It does not set __wrapped__, so
+    # inspect cannot unwrap it to get back to the original function.
+    def __init__(self, func):
+        self.__code__ = func.__code__
+
+    def __get__(self, instance, owner=None):
+        if instance is None:
+            return self
+        return MethodLike(self, instance)
+
+class MethodLike:
+    # Provides __func__, but is not an instance of types.MethodType.
+    def __init__(self, func, instance):
+        self.__func__ = func
+        self.__self__ = instance
+
+# line 422
+@FunctionLike
+def func424():
+    return 425
+
+# line 427
+class cls428:
+    @FunctionLike
+    def func430(self):
+        return 431
+
 pass # end of file

Lib/test/test_inspect/test_inspect.py

@@ -1039,6 +1039,14 @@ def test_getsource_unwrap(self):
     def test_decorator_with_lambda(self):
         self.assertSourceEqual(mod2.func114, 113, 115)
 
+    def test_function_like_decorator(self):
+        # Test duck-typed functions and methods (as dummies for Cython functions)
+        self.assertEqual(inspect.getfile(mod2.func424), mod2.__file__)
+        self.assertSourceEqual(mod2.func424, 423, 425)
+        method = mod2.cls428().func430
+        self.assertEqual(inspect.getfile(method), mod2.__file__)
+        self.assertSourceEqual(method, 429, 431)
+
 class TestOneliners(GetSourceBase):
     fodderModule = mod2
     def test_oneline_lambda(self):

Misc/NEWS.d/next/Core_and_Builtins/2025-03-23-14-13-20.gh-issue-131628.M9Q06m.rst

@@ -0,0 +1 @@
+Use duck-typing in ``inspect`` to support Cython functions in ``getfile`` and ``getsource``