[3.13] gh-121027: Add a future warning in functools.partial.__get__ (GH-121086) (#121092)

gh-121027: Add a future warning in functools.partial.__get__ (GH-121086)
(cherry picked from commit db96edd6d1a58045196a71aff565743f493b5fbb)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>

4 files changed, 51 insertions, 17 deletions

diff --git a/Lib/functools.py b/Lib/functools.py
index 3d0fd66..d04957c 100644
--- a/Lib/functools.py
+++ b/Lib/functools.py
@@ -311,6 +311,16 @@ class partial:
         args.extend(f"{k}={v!r}" for (k, v) in self.keywords.items())
         return f"{module}.{qualname}({', '.join(args)})"
 
+    def __get__(self, obj, objtype=None):
+        if obj is None:
+            return self
+        import warnings
+        warnings.warn('functools.partial will be a method descriptor in '
+                      'future Python versions; wrap it in staticmethod() '
+                      'if you want to preserve the old behavior',
+                      FutureWarning, 2)
+        return self
+
     def __reduce__(self):
         return type(self), (self.func,), (self.func, self.args,
                self.keywords or None, self.__dict__ or None)
@@ -392,7 +402,7 @@ class partialmethod(object):
     def __get__(self, obj, cls=None):
         get = getattr(self.func, "__get__", None)
         result = None
-        if get is not None:
+        if get is not None and not isinstance(self.func, partial):
             new_func = get(obj, cls)
             if new_func is not self.func:
                 # Assume __get__ returning something new indicates the
diff --git a/Lib/inspect.py b/Lib/inspect.py
index 2c82ad5..bf979e8 100644
--- a/Lib/inspect.py
+++ b/Lib/inspect.py
@@ -2556,6 +2556,10 @@ def _signature_from_callable(obj, *,
                 new_params = (first_wrapped_param,) + sig_params
                 return sig.replace(parameters=new_params)
 
+    if isinstance(obj, functools.partial):
+        wrapped_sig = _get_signature_of(obj.func)
+        return _signature_get_partial(wrapped_sig, obj)
+
     if isfunction(obj) or _signature_is_functionlike(obj):
         # If it's a pure Python function, or an object that is duck type
         # of a Python function (Cython functions, for instance), then:
@@ -2567,10 +2571,6 @@ def _signature_from_callable(obj, *,
         return _signature_from_builtin(sigcls, obj,
                                        skip_bound_arg=skip_bound_arg)
 
-    if isinstance(obj, functools.partial):
-        wrapped_sig = _get_signature_of(obj.func)
-        return _signature_get_partial(wrapped_sig, obj)
-
     if isinstance(obj, type):
         # obj is a class or a metaclass
 
diff --git a/Lib/test/test_functools.py b/Lib/test/test_functools.py
index 559213f..1ce0f4d 100644
--- a/Lib/test/test_functools.py
+++ b/Lib/test/test_functools.py
@@ -395,6 +395,23 @@ class TestPartial:
         f = self.partial(object)
         self.assertRaises(TypeError, f.__setstate__, BadSequence())
 
+    def test_partial_as_method(self):
+        class A:
+            meth = self.partial(capture, 1, a=2)
+            cmeth = classmethod(self.partial(capture, 1, a=2))
+            smeth = staticmethod(self.partial(capture, 1, a=2))
+
+        a = A()
+        self.assertEqual(A.meth(3, b=4), ((1, 3), {'a': 2, 'b': 4}))
+        self.assertEqual(A.cmeth(3, b=4), ((1, A, 3), {'a': 2, 'b': 4}))
+        self.assertEqual(A.smeth(3, b=4), ((1, 3), {'a': 2, 'b': 4}))
+        with self.assertWarns(FutureWarning) as w:
+            self.assertEqual(a.meth(3, b=4), ((1, 3), {'a': 2, 'b': 4}))
+        self.assertEqual(w.filename, __file__)
+        self.assertEqual(a.cmeth(3, b=4), ((1, A, 3), {'a': 2, 'b': 4}))
+        self.assertEqual(a.smeth(3, b=4), ((1, 3), {'a': 2, 'b': 4}))
+
+
 @unittest.skipUnless(c_functools, 'requires the C _functools module')
 class TestPartialC(TestPartial, unittest.TestCase):
     if c_functools:
diff --git a/Lib/test/test_inspect/test_inspect.py b/Lib/test/test_inspect/test_inspect.py
index 34739b6..5d0f328 100644
--- a/Lib/test/test_inspect/test_inspect.py
+++ b/Lib/test/test_inspect/test_inspect.py
@@ -3873,10 +3873,12 @@ class TestSignatureObject(unittest.TestCase):
                 def __init__(self, b):
                     pass
 
-            self.assertEqual(C(1), (2, 1))
-            self.assertEqual(self.signature(C),
-                            ((('a', ..., ..., "positional_or_keyword"),),
-                            ...))
+            with self.assertWarns(FutureWarning):
+                self.assertEqual(C(1), (2, 1))
+            with self.assertWarns(FutureWarning):
+                self.assertEqual(self.signature(C),
+                                ((('a', ..., ..., "positional_or_keyword"),),
+                                ...))
 
         with self.subTest('partialmethod'):
             class CM(type):
@@ -4024,10 +4026,12 @@ class TestSignatureObject(unittest.TestCase):
             class C:
                 __init__ = functools.partial(lambda x, a: None, 2)
 
-            C(1)  # does not raise
-            self.assertEqual(self.signature(C),
-                            ((('a', ..., ..., "positional_or_keyword"),),
-                            ...))
+            with self.assertWarns(FutureWarning):
+                C(1)  # does not raise
+            with self.assertWarns(FutureWarning):
+                self.assertEqual(self.signature(C),
+                                ((('a', ..., ..., "positional_or_keyword"),),
+                                ...))
 
         with self.subTest('partialmethod'):
             class C:
@@ -4282,10 +4286,13 @@ class TestSignatureObject(unittest.TestCase):
             class C:
                 __call__ = functools.partial(lambda x, a: (x, a), 2)
 
-            self.assertEqual(C()(1), (2, 1))
-            self.assertEqual(self.signature(C()),
-                            ((('a', ..., ..., "positional_or_keyword"),),
-                            ...))
+            c = C()
+            with self.assertWarns(FutureWarning):
+                self.assertEqual(c(1), (2, 1))
+            with self.assertWarns(FutureWarning):
+                self.assertEqual(self.signature(c),
+                                ((('a', ..., ..., "positional_or_keyword"),),
+                                ...))
 
         with self.subTest('partialmethod'):
             class C: