gh-112006: Fix inspect.unwrap() for types where __wrapped__ is a data descriptor (GH-115540)

This also fixes inspect.Signature.from_callable() for builtins classmethod()
and staticmethod().

Author: serhiy-storchaka

Lib/inspect.py

@@ -762,18 +762,14 @@ def unwrap(func, *, stop=None):
    :exc:`ValueError` is raised if a cycle is encountered.
 
     """
-    if stop is None:
-        def _is_wrapper(f):
-            return hasattr(f, '__wrapped__')
-    else:
-        def _is_wrapper(f):
-            return hasattr(f, '__wrapped__') and not stop(f)
     f = func  # remember the original func for error reporting
     # Memoise by id to tolerate non-hashable objects, but store objects to
     # ensure they aren't destroyed, which would allow their IDs to be reused.
     memo = {id(f): f}
     recursion_limit = sys.getrecursionlimit()
-    while _is_wrapper(func):
+    while not isinstance(func, type) and hasattr(func, '__wrapped__'):
+        if stop is not None and stop(func):
+            break
         func = func.__wrapped__
         id_func = id(func)
         if (id_func in memo) or (len(memo) >= recursion_limit):

Lib/test/test_inspect/test_inspect.py

@@ -3137,6 +3137,10 @@ def m1d(*args, **kwargs):
                           int))
 
     def test_signature_on_classmethod(self):
+        self.assertEqual(self.signature(classmethod),
+                         ((('function', ..., ..., "positional_only"),),
+                          ...))
+
         class Test:
             @classmethod
             def foo(cls, arg1, *, arg2=1):
@@ -3155,6 +3159,10 @@ def foo(cls, arg1, *, arg2=1):
                           ...))
 
     def test_signature_on_staticmethod(self):
+        self.assertEqual(self.signature(staticmethod),
+                         ((('function', ..., ..., "positional_only"),),
+                          ...))
+
         class Test:
             @staticmethod
             def foo(cls, *, arg):
@@ -3678,16 +3686,20 @@ class Bar(Spam, Foo):
                          ((('a', ..., ..., "positional_or_keyword"),),
                           ...))
 
-        class Wrapped:
-            pass
-        Wrapped.__wrapped__ = lambda a: None
-        self.assertEqual(self.signature(Wrapped),
+    def test_signature_on_wrapper(self):
+        class Wrapper:
+            def __call__(self, b):
+                pass
+        wrapper = Wrapper()
+        wrapper.__wrapped__ = lambda a: None
+        self.assertEqual(self.signature(wrapper),
                          ((('a', ..., ..., "positional_or_keyword"),),
                           ...))
         # wrapper loop:
-        Wrapped.__wrapped__ = Wrapped
+        wrapper = Wrapper()
+        wrapper.__wrapped__ = wrapper
         with self.assertRaisesRegex(ValueError, 'wrapper loop'):
-            self.signature(Wrapped)
+            self.signature(wrapper)
 
     def test_signature_on_lambdas(self):
         self.assertEqual(self.signature((lambda a=10: a)),
@@ -4999,6 +5011,14 @@ def test_recursion_limit(self):
         with self.assertRaisesRegex(ValueError, 'wrapper loop'):
             inspect.unwrap(obj)
 
+    def test_wrapped_descriptor(self):
+        self.assertIs(inspect.unwrap(NTimesUnwrappable), NTimesUnwrappable)
+        self.assertIs(inspect.unwrap(staticmethod), staticmethod)
+        self.assertIs(inspect.unwrap(classmethod), classmethod)
+        self.assertIs(inspect.unwrap(staticmethod(classmethod)), classmethod)
+        self.assertIs(inspect.unwrap(classmethod(staticmethod)), staticmethod)
+
+
 class TestMain(unittest.TestCase):
     def test_only_source(self):
         module = importlib.import_module('unittest')

Misc/NEWS.d/next/Library/2024-02-15-23-42-54.gh-issue-112006.4wxcK-.rst

@@ -0,0 +1,3 @@
+Fix :func:`inspect.unwrap` for types with the ``__wrapper__`` data
+descriptor. Fix :meth:`inspect.Signature.from_callable` for builtins
+:func:`classmethod` and :func:`staticmethod`.