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Issue #13575: there is only one class type.

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Florent Xicluna 2011-12-12 18:54:29 +01:00
parent 9d57481f04
commit aa6c1d240f
8 changed files with 25 additions and 81 deletions
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12
Doc/howto/descriptor.rst
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@ -36,9 +36,7 @@ continuing through the base classes of ``type(a)`` excluding metaclasses. If the
looked-up value is an object defining one of the descriptor methods, then Python
may override the default behavior and invoke the descriptor method instead.
Where this occurs in the precedence chain depends on which descriptor methods
were defined. Note that descriptors are only invoked for new style objects or
classes (a class is new style if it inherits from :class:`object` or
:class:`type`).
were defined.
Descriptors are a powerful, general purpose protocol. They are the mechanism
behind properties, methods, static methods, class methods, and :func:`super()`.
@ -89,8 +87,6 @@ of ``obj``. If ``d`` defines the method :meth:`__get__`, then ``d.__get__(obj)`
is invoked according to the precedence rules listed below.
The details of invocation depend on whether ``obj`` is an object or a class.
Either way, descriptors only work for new style objects and classes. A class is
new style if it is a subclass of :class:`object`.
For objects, the machinery is in :meth:`object.__getattribute__` which
transforms ``b.x`` into ``type(b).__dict__['x'].__get__(b, type(b))``. The
@ -115,7 +111,6 @@ The important points to remember are:
* descriptors are invoked by the :meth:`__getattribute__` method
* overriding :meth:`__getattribute__` prevents automatic descriptor calls
* :meth:`__getattribute__` is only available with new style classes and objects
* :meth:`object.__getattribute__` and :meth:`type.__getattribute__` make
different calls to :meth:`__get__`.
* data descriptors always override instance dictionaries.
@ -128,10 +123,7 @@ and then returns ``A.__dict__['m'].__get__(obj, A)``. If not a descriptor,
``m`` is returned unchanged. If not in the dictionary, ``m`` reverts to a
search using :meth:`object.__getattribute__`.
Note, in Python 2.2, ``super(B, obj).m()`` would only invoke :meth:`__get__` if
``m`` was a data descriptor. In Python 2.3, non-data descriptors also get
invoked unless an old-style class is involved. The implementation details are
in :c:func:`super_getattro()` in
The implementation details are in :c:func:`super_getattro()` in
`Objects/typeobject.c <http://svn.python.org/view/python/trunk/Objects/typeobject.c?view=markup>`_
and a pure Python equivalent can be found in `Guido's Tutorial`_.