mirror of https://github.com/python/cpython
gh-121027: Add a future warning in functools.partial.__get__ (#121086)
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@ -2262,6 +2262,12 @@ Changes in the Python API
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returned by :meth:`zipfile.ZipFile.open` was changed from ``'r'`` to ``'rb'``.
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(Contributed by Serhiy Storchaka in :gh:`115961`.)
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* :class:`functools.partial` now emits a :exc:`FutureWarning` when it is
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used as a method.
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Its behavior will be changed in future Python versions.
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Wrap it in :func:`staticmethod` if you want to preserve the old behavior.
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(Contributed by Serhiy Storchaka in :gh:`121027`.)
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.. _pep667-porting-notes-py:
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* Calling :func:`locals` in an :term:`optimized scope` now produces an
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@ -311,6 +311,16 @@ class partial:
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args.extend(f"{k}={v!r}" for (k, v) in self.keywords.items())
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return f"{module}.{qualname}({', '.join(args)})"
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def __get__(self, obj, objtype=None):
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if obj is None:
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return self
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import warnings
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warnings.warn('functools.partial will be a method descriptor in '
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'future Python versions; wrap it in staticmethod() '
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'if you want to preserve the old behavior',
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FutureWarning, 2)
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return self
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def __reduce__(self):
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return type(self), (self.func,), (self.func, self.args,
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self.keywords or None, self.__dict__ or None)
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@ -392,7 +402,7 @@ class partialmethod(object):
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def __get__(self, obj, cls=None):
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get = getattr(self.func, "__get__", None)
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result = None
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if get is not None:
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if get is not None and not isinstance(self.func, partial):
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new_func = get(obj, cls)
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if new_func is not self.func:
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# Assume __get__ returning something new indicates the
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@ -2550,6 +2550,10 @@ def _signature_from_callable(obj, *,
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new_params = (first_wrapped_param,) + sig_params
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return sig.replace(parameters=new_params)
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if isinstance(obj, functools.partial):
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wrapped_sig = _get_signature_of(obj.func)
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return _signature_get_partial(wrapped_sig, obj)
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if isfunction(obj) or _signature_is_functionlike(obj):
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# If it's a pure Python function, or an object that is duck type
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# of a Python function (Cython functions, for instance), then:
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@ -2561,10 +2565,6 @@ def _signature_from_callable(obj, *,
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return _signature_from_builtin(sigcls, obj,
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skip_bound_arg=skip_bound_arg)
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if isinstance(obj, functools.partial):
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wrapped_sig = _get_signature_of(obj.func)
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return _signature_get_partial(wrapped_sig, obj)
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if isinstance(obj, type):
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# obj is a class or a metaclass
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@ -395,6 +395,23 @@ class TestPartial:
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f = self.partial(object)
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self.assertRaises(TypeError, f.__setstate__, BadSequence())
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def test_partial_as_method(self):
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class A:
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meth = self.partial(capture, 1, a=2)
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cmeth = classmethod(self.partial(capture, 1, a=2))
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smeth = staticmethod(self.partial(capture, 1, a=2))
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a = A()
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self.assertEqual(A.meth(3, b=4), ((1, 3), {'a': 2, 'b': 4}))
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self.assertEqual(A.cmeth(3, b=4), ((1, A, 3), {'a': 2, 'b': 4}))
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self.assertEqual(A.smeth(3, b=4), ((1, 3), {'a': 2, 'b': 4}))
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with self.assertWarns(FutureWarning) as w:
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self.assertEqual(a.meth(3, b=4), ((1, 3), {'a': 2, 'b': 4}))
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self.assertEqual(w.filename, __file__)
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self.assertEqual(a.cmeth(3, b=4), ((1, A, 3), {'a': 2, 'b': 4}))
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self.assertEqual(a.smeth(3, b=4), ((1, 3), {'a': 2, 'b': 4}))
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@unittest.skipUnless(c_functools, 'requires the C _functools module')
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class TestPartialC(TestPartial, unittest.TestCase):
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if c_functools:
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@ -3873,10 +3873,12 @@ class TestSignatureObject(unittest.TestCase):
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def __init__(self, b):
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pass
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self.assertEqual(C(1), (2, 1))
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self.assertEqual(self.signature(C),
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((('a', ..., ..., "positional_or_keyword"),),
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...))
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with self.assertWarns(FutureWarning):
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self.assertEqual(C(1), (2, 1))
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with self.assertWarns(FutureWarning):
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self.assertEqual(self.signature(C),
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((('a', ..., ..., "positional_or_keyword"),),
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...))
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with self.subTest('partialmethod'):
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class CM(type):
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@ -4024,10 +4026,12 @@ class TestSignatureObject(unittest.TestCase):
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class C:
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__init__ = functools.partial(lambda x, a: None, 2)
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C(1) # does not raise
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self.assertEqual(self.signature(C),
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((('a', ..., ..., "positional_or_keyword"),),
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...))
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with self.assertWarns(FutureWarning):
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C(1) # does not raise
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with self.assertWarns(FutureWarning):
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self.assertEqual(self.signature(C),
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((('a', ..., ..., "positional_or_keyword"),),
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...))
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with self.subTest('partialmethod'):
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class C:
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@ -4282,10 +4286,13 @@ class TestSignatureObject(unittest.TestCase):
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class C:
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__call__ = functools.partial(lambda x, a: (x, a), 2)
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self.assertEqual(C()(1), (2, 1))
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self.assertEqual(self.signature(C()),
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((('a', ..., ..., "positional_or_keyword"),),
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...))
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c = C()
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with self.assertWarns(FutureWarning):
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self.assertEqual(c(1), (2, 1))
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with self.assertWarns(FutureWarning):
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self.assertEqual(self.signature(c),
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((('a', ..., ..., "positional_or_keyword"),),
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...))
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with self.subTest('partialmethod'):
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class C:
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@ -0,0 +1,2 @@
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Add a future warning in :meth:`!functools.partial.__get__`. In future Python
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versions :class:`functools.partial` will be a method descriptor.
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@ -197,6 +197,21 @@ partial_dealloc(partialobject *pto)
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Py_DECREF(tp);
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}
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static PyObject *
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partial_descr_get(PyObject *self, PyObject *obj, PyObject *type)
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{
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if (obj == Py_None || obj == NULL) {
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return Py_NewRef(self);
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}
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if (PyErr_WarnEx(PyExc_FutureWarning,
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"functools.partial will be a method descriptor in "
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"future Python versions; wrap it in staticmethod() "
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"if you want to preserve the old behavior", 1) < 0)
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{
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return NULL;
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}
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return Py_NewRef(self);
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}
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/* Merging keyword arguments using the vectorcall convention is messy, so
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* if we would need to do that, we stop using vectorcall and fall back
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@ -514,6 +529,7 @@ static PyType_Slot partial_type_slots[] = {
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{Py_tp_methods, partial_methods},
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{Py_tp_members, partial_memberlist},
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{Py_tp_getset, partial_getsetlist},
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{Py_tp_descr_get, (descrgetfunc)partial_descr_get},
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{Py_tp_new, partial_new},
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{Py_tp_free, PyObject_GC_Del},
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{0, 0}
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