gh-121027: Make the functools.partial object a method descriptor

serhiy-storchaka · d.grigonis · serhiy-storchaka · commit 693fbc782dd0 · 2024-06-27T14:23:27.000+03:00
Co-authored-by: d.grigonis &lt;dgrigonis@users.noreply.github.com&gt;
diff --git a/Doc/whatsnew/3.14.rst b/Doc/whatsnew/3.14.rst
@@ -292,6 +292,12 @@ Porting to Python 3.14
 This section lists previously described changes and other bugfixes
 that may require changes to your code.
 
+Changes in the Python API
+-------------------------
+
+* :class:`functools.partial` is now a method descriptor.
+ Wrap it in :func:`staticmethod` if you want to preserve the old behavior.
+ (Contributed by Serhiy Storchaka and D. Grigonis in :gh:`121027`.)
 
 Build Changes
 =============
diff --git a/Lib/functools.py b/Lib/functools.py
@@ -18,6 +18,7 @@
 from collections import namedtuple
 # import types, weakref # Deferred to single_dispatch()
 from reprlib import recursive_repr
+from types import MethodType
 from _thread import RLock
 
 # Avoid importing types, so we can speedup import time
@@ -314,12 +315,7 @@ def __repr__(self):
 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
+ return MethodType(self, obj)
 
 def __reduce__(self):
 return type(self), (self.func,), (self.func, self.args,
@@ -402,7 +398,7 @@ def _method(cls_or_self, /, *args, **keywords):
 def __get__(self, obj, cls=None):
 get = getattr(self.func, "__get__", None)
 result = None
- if get is not None and not isinstance(self.func, partial):
+ if get is not None:
 new_func = get(obj, cls)
 if new_func is not self.func:
 # Assume __get__ returning something new indicates the
diff --git a/Lib/test/test_functools.py b/Lib/test/test_functools.py
@@ -405,9 +405,7 @@ class 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.meth(3, b=4), ((1, a, 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}))
 
diff --git a/Lib/test/test_inspect/test_inspect.py b/Lib/test/test_inspect/test_inspect.py
@@ -3868,17 +3868,15 @@ def __init__(self, b):
 
 with self.subTest('partial'):
 class CM(type):
- __call__ = functools.partial(lambda x, a: (x, a), 2)
+ __call__ = functools.partial(lambda x, a, b: (x, a, b), 2)
 class C(metaclass=CM):
- def __init__(self, b):
+ def __init__(self, c):
 pass
 
- with self.assertWarns(FutureWarning):
- self.assertEqual(C(1), (2, 1))
- with self.assertWarns(FutureWarning):
- self.assertEqual(self.signature(C),
- ((('a', ..., ..., "positional_or_keyword"),),
- ...))
+ self.assertEqual(C(1), (2, C, 1))
+ self.assertEqual(self.signature(C),
+ ((('b', ..., ..., "positional_or_keyword"),),
+ ...))
 
 with self.subTest('partialmethod'):
 class CM(type):
@@ -4024,14 +4022,12 @@ class C:
 
 with self.subTest('partial'):
 class C:
- __init__ = functools.partial(lambda x, a: None, 2)
+ __init__ = functools.partial(lambda x, a, b: None, 2)
 
- with self.assertWarns(FutureWarning):
- C(1) # does not raise
- with self.assertWarns(FutureWarning):
- self.assertEqual(self.signature(C),
- ((('a', ..., ..., "positional_or_keyword"),),
- ...))
+ C(1) # does not raise
+ self.assertEqual(self.signature(C),
+ ((('b', ..., ..., "positional_or_keyword"),),
+ ...))
 
 with self.subTest('partialmethod'):
 class C:
@@ -4284,15 +4280,13 @@ class C:
 
 with self.subTest('partial'):
 class C:
- __call__ = functools.partial(lambda x, a: (x, a), 2)
+ __call__ = functools.partial(lambda x, a, b: (x, a, b), 2)
 
 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"),),
- ...))
+ self.assertEqual(c(1), (2, c, 1))
+ self.assertEqual(self.signature(C()),
+ ((('b', ..., ..., "positional_or_keyword"),),
+ ...))
 
 with self.subTest('partialmethod'):
 class C:
diff --git a/Misc/NEWS.d/next/Library/2024-06-27-12-27-52.gh-issue-121027.D4K1OX.rst b/Misc/NEWS.d/next/Library/2024-06-27-12-27-52.gh-issue-121027.D4K1OX.rst
@@ -0,0 +1 @@
+Make the :class:`functools.partial` object a method descriptor.
diff --git a/Modules/_functoolsmodule.c b/Modules/_functoolsmodule.c
@@ -203,14 +203,7 @@ partial_descr_get(PyObject *self, PyObject *obj, PyObject *type)
 if (obj == Py_None || obj == NULL){
 return Py_NewRef(self);
 }
- if (PyErr_WarnEx(PyExc_FutureWarning,
- "functools.partial will be a method descriptor in "
- "future Python versions; wrap it in staticmethod() "
- "if you want to preserve the old behavior", 1) < 0)
-{
- return NULL;
- }
- return Py_NewRef(self);
+ return PyMethod_New(self, obj);
 }
 
 /* Merging keyword arguments using the vectorcall convention is messy, so

-Original file line number
+Diff line change
 fromcollectionsimportnamedtuple
 # import types, weakref # Deferred to single_dispatch()
 fromreprlibimportrecursive_repr
 +fromtypesimportMethodType
 from_threadimportRLock
 # Avoid importing types, so we can speedup import time
 def__get__(self, obj, objtype=None):
 ifobjisNone:
 returnself
 -importwarnings
 -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)
 -returnself
 +returnMethodType(self, obj)
 def__reduce__(self):
 returntype(self), (self.func,), (self.func, self.args,
 def__get__(self, obj, cls=None):
 get=getattr(self.func, "__get__", None)
 result=None
 -ifgetisnotNoneandnotisinstance(self.func, partial):
 +ifgetisnotNone:
 new_func=get(obj, cls)
 ifnew_funcisnotself.func:
 # Assume __get__ returning something new indicates the
-Original file line number
+Diff line change
 withself.subTest('partial'):
 classCM(type):
 -__call__=functools.partial(lambdax, a: (x, a), 2)
 +__call__=functools.partial(lambdax, a, b: (x, a, b), 2)
 classC(metaclass=CM):
 -def__init__(self, b):
 +def__init__(self, c):
 pass
 -withself.assertWarns(FutureWarning):
 -self.assertEqual(C(1), (2, 1))
 -withself.assertWarns(FutureWarning):
 -self.assertEqual(self.signature(C),
 - ((('a', ..., ..., "positional_or_keyword"),),
 - ...))
 +self.assertEqual(C(1), (2, C, 1))
 +self.assertEqual(self.signature(C),
 + ((('b', ..., ..., "positional_or_keyword"),),
 + ...))
 withself.subTest('partialmethod'):
 classCM(type):
 withself.subTest('partial'):
 classC:
 -__init__=functools.partial(lambdax, a: None, 2)
 +__init__=functools.partial(lambdax, a, b: None, 2)
 -withself.assertWarns(FutureWarning):
 -C(1) # does not raise
 -withself.assertWarns(FutureWarning):
 -self.assertEqual(self.signature(C),
 - ((('a', ..., ..., "positional_or_keyword"),),
 - ...))
 +C(1) # does not raise
 +self.assertEqual(self.signature(C),
 + ((('b', ..., ..., "positional_or_keyword"),),
 + ...))
 withself.subTest('partialmethod'):
 classC:
 withself.subTest('partial'):
 classC:
 -__call__=functools.partial(lambdax, a: (x, a), 2)
 +__call__=functools.partial(lambdax, a, b: (x, a, b), 2)
 c=C()
 -withself.assertWarns(FutureWarning):
 -self.assertEqual(c(1), (2, 1))
 -withself.assertWarns(FutureWarning):
 -self.assertEqual(self.signature(c),
 - ((('a', ..., ..., "positional_or_keyword"),),
 - ...))
 +self.assertEqual(c(1), (2, c, 1))
 +self.assertEqual(self.signature(C()),
 + ((('b', ..., ..., "positional_or_keyword"),),
 + ...))
 withself.subTest('partialmethod'):
 classC:
Original file line number	Diff line number	Diff line change
`@@ -0,0 +1 @@`
	`1`	+Make the :class:`functools.partial` object a method descriptor.