gh-101860: Expose __name__ on property

Useful for introspection and consistent with functions and other
descriptors.

Author: eltoder

Doc/howto/descriptor.rst

@@ -1004,47 +1004,50 @@ here is a pure Python equivalent:
             if doc is None and fget is not None:
                 doc = fget.__doc__
             self.__doc__ = doc
-            self._name = ''
+            self.__name__ = None
 
         def __set_name__(self, owner, name):
-            self._name = name
+            self.__name__ = name
 
         def __get__(self, obj, objtype=None):
             if obj is None:
                 return self
             if self.fget is None:
                 raise AttributeError(
-                    f'property {self._name!r} of {type(obj).__name__!r} object has no getter'
+                    f'property {self.__name__!r} of {type(obj).__name__!r} '
+                    'object has no getter'
                  )
             return self.fget(obj)
 
         def __set__(self, obj, value):
             if self.fset is None:
                 raise AttributeError(
-                    f'property {self._name!r} of {type(obj).__name__!r} object has no setter'
+                    f'property {self.__name__!r} of {type(obj).__name__!r} '
+                    'object has no setter'
                  )
             self.fset(obj, value)
 
         def __delete__(self, obj):
             if self.fdel is None:
                 raise AttributeError(
-                    f'property {self._name!r} of {type(obj).__name__!r} object has no deleter'
+                    f'property {self.__name__!r} of {type(obj).__name__!r} '
+                    'object has no deleter'
                  )
             self.fdel(obj)
 
         def getter(self, fget):
             prop = type(self)(fget, self.fset, self.fdel, self.__doc__)
-            prop._name = self._name
+            prop.__name__ = self.__name__
             return prop
 
         def setter(self, fset):
             prop = type(self)(self.fget, fset, self.fdel, self.__doc__)
-            prop._name = self._name
+            prop.__name__ = self.__name__
             return prop
 
         def deleter(self, fdel):
             prop = type(self)(self.fget, self.fset, fdel, self.__doc__)
-            prop._name = self._name
+            prop.__name__ = self.__name__
             return prop
 
 .. testcode::

Lib/inspect.py

@@ -834,9 +834,8 @@ def _finddoc(obj):
             cls = self.__class__
     # Should be tested before isdatadescriptor().
     elif isinstance(obj, property):
-        func = obj.fget
-        name = func.__name__
-        cls = _findclass(func)
+        name = obj.__name__
+        cls = _findclass(obj.fget)
         if cls is None or getattr(cls, name) is not obj:
             return None
     elif ismethoddescriptor(obj) or isdatadescriptor(obj):

Lib/pydoc.py

@@ -127,9 +127,8 @@ def _finddoc(obj):
             cls = self.__class__
     # Should be tested before isdatadescriptor().
     elif isinstance(obj, property):
-        func = obj.fget
-        name = func.__name__
-        cls = _findclass(func)
+        name = obj.__name__
+        cls = _findclass(obj.fget)
         if cls is None or getattr(cls, name) is not obj:
             return None
     elif inspect.ismethoddescriptor(obj) or inspect.isdatadescriptor(obj):

Lib/test/test_inspect/inspect_fodder.py

@@ -68,9 +68,9 @@ class FesteringGob(MalodorousPervert, ParrotDroppings):
     def abuse(self, a, b, c):
         pass
 
-    @property
-    def contradiction(self):
+    def _getter(self):
         pass
+    contradiction = property(_getter)
 
 async def lobbest(grenade):
     pass

Lib/test/test_property.py

@@ -183,6 +183,26 @@ def test_refleaks_in___init__(self):
             fake_prop.__init__('fget', 'fset', 'fdel', 'doc')
         self.assertAlmostEqual(gettotalrefcount() - refs_before, 0, delta=10)
 
+    def test_property_name(self):
+        def getter(self):
+            return 42
+
+        class A:
+            @property
+            def foo(self):
+                return 1
+
+            bar = property(getter)
+
+        self.assertEqual(A.foo.__name__, 'foo')
+        self.assertEqual(A.bar.__name__, 'bar')
+
+        A.baz = property(getter)
+        self.assertIsNone(A.baz.__name__)
+        A.baz.__name__ = 'mybaz'
+        self.assertEqual(A.baz.__name__, 'mybaz')
+        self.assertEqual(A.bar.__name__, 'bar')  # not affected
+
     def test_property_set_name_incorrect_args(self):
         p = property()
 

Lib/test/test_pydoc/test_pydoc.py

@@ -1162,6 +1162,17 @@ def test_importfile(self):
         self.assertEqual(loaded_pydoc.__spec__, pydoc.__spec__)
 
 
+class Rect:
+    @property
+    def area(self):
+        '''Area of the rect'''
+        return self.w * self.h
+
+
+class Square(Rect):
+    area = property(lambda self: self.side**2)
+
+
 class TestDescriptions(unittest.TestCase):
 
     def test_module(self):
@@ -1550,13 +1561,13 @@ def test_namedtuple_field_descriptor(self):
 
     @requires_docstrings
     def test_property(self):
-        class Rect:
-            @property
-            def area(self):
-                '''Area of the rect'''
-                return self.w * self.h
-
         self.assertEqual(self._get_summary_lines(Rect.area), """\
+area
+    Area of the rect
+""")
+        # inherits the docstring from Rect.area
+        self.assertEqual(self._get_summary_lines(Square.area), """\
+area
     Area of the rect
 """)
         self.assertIn("""

Misc/NEWS.d/next/Core and Builtins/2023-02-13-11-36-50.gh-issue-101860.CKCMbC.rst

@@ -0,0 +1 @@
+Expose ``__name__`` attribute on property.

Objects/descrobject.c

@@ -1519,6 +1519,10 @@ class property(object):
             self.__doc__ = doc
         except AttributeError:  # read-only or dict-less class
             pass
+        self.__name__ = None
+
+    def __set_name__(self, owner, name):
+        self.__name__ = name
 
     def __get__(self, inst, type=None):
         if inst is None:
@@ -1547,6 +1551,7 @@ static PyMemberDef property_members[] = {
     {"fset", _Py_T_OBJECT, offsetof(propertyobject, prop_set), Py_READONLY},
     {"fdel", _Py_T_OBJECT, offsetof(propertyobject, prop_del), Py_READONLY},
     {"__doc__",  _Py_T_OBJECT, offsetof(propertyobject, prop_doc), 0},
+    {"__name__", _Py_T_OBJECT, offsetof(propertyobject, prop_name), 0},
     {0}
 };