Minor edits to the Descriptor HowTo Guide

Doc/howto/descriptor.rst

@@ -847,7 +847,7 @@ afterwards, :meth:`__set_name__` will need to be called manually.
 ORM example
 -----------
 
-The following code is simplified skeleton showing how data descriptors could
+The following code is a simplified skeleton showing how data descriptors could
 be used to implement an `object relational mapping
 <https://en.wikipedia.org/wiki/Object%E2%80%93relational_mapping>`_.
 
@@ -1535,6 +1535,8 @@ by member descriptors:
  def __get__(self, obj, objtype=None):
  'Emulate member_get() in Objects/descrobject.c'
  # Also see PyMember_GetOne() in Python/structmember.c
+ if obj is None:
+ return self
  value = obj._slotvalues[self.offset]
  if value is null:
  raise AttributeError(self.name)
@@ -1563,13 +1565,13 @@ variables:
  class Type(type):
  'Simulate how the type metaclass adds member objects for slots'
 
- def __new__(mcls, clsname, bases, mapping):
+ def __new__(mcls, clsname, bases, mapping, **kwargs):
  'Emulate type_new() in Objects/typeobject.c'
  # type_new() calls PyTypeReady() which calls add_methods()
  slot_names = mapping.get('slot_names', [])
  for offset, name in enumerate(slot_names):
  mapping[name] = Member(name, clsname, offset)
- return type.__new__(mcls, clsname, bases, mapping)
+ return type.__new__(mcls, clsname, bases, mapping, **kwargs)
 
 The :meth:`object.__new__` method takes care of creating instances that have
 slots instead of an instance dictionary. Here is a rough simulation in pure
@@ -1580,7 +1582,7 @@ Python:
  class Object:
  'Simulate how object.__new__() allocates memory for __slots__'
 
- def __new__(cls, *args):
+ def __new__(cls, *args, **kwargs):
  'Emulate object_new() in Objects/typeobject.c'
  inst = super().__new__(cls)
  if hasattr(cls, 'slot_names'):
@@ -1593,7 +1595,7 @@ Python:
  cls = type(self)
  if hasattr(cls, 'slot_names') and name not in cls.slot_names:
  raise AttributeError(
- f'{type(self).__name__!r} object has no attribute{name!r}'
+ f'{cls.__name__!r} object has no attribute{name!r}'
  )
  super().__setattr__(name, value)
 
@@ -1602,7 +1604,7 @@ Python:
  cls = type(self)
  if hasattr(cls, 'slot_names') and name not in cls.slot_names:
  raise AttributeError(
- f'{type(self).__name__!r} object has no attribute{name!r}'
+ f'{cls.__name__!r} object has no attribute{name!r}'
  )
  super().__delattr__(name)