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#2567: remove new-style/old-style class docs.

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Georg Brandl 2008-04-07 19:17:06 +00:00
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Doc/reference/datamodel.rst
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@ -980,45 +980,6 @@ Internal types
by the built-in :func:`classmethod` constructor.
.. _newstyle:
New-style and classic classes
=============================
Classes and instances come in two flavors: old-style or classic, and new-style.
Up to Python 2.1, old-style classes were the only flavour available to the user.
The concept of (old-style) class is unrelated to the concept of type: if *x* is
an instance of an old-style class, then ``x.__class__`` designates the class of
*x*, but ``type(x)`` is always ``<type 'instance'>``. This reflects the fact
that all old-style instances, independently of their class, are implemented with
a single built-in type, called ``instance``.
New-style classes were introduced in Python 2.2 to unify classes and types. A
new-style class is neither more nor less than a user-defined type. If *x* is an
instance of a new-style class, then ``type(x)`` is the same as ``x.__class__``.
The major motivation for introducing new-style classes is to provide a unified
object model with a full meta-model. It also has a number of immediate
benefits, like the ability to subclass most built-in types, or the introduction
of "descriptors", which enable computed properties.
For compatibility reasons, classes are still old-style by default. New-style
classes are created by specifying another new-style class (i.e. a type) as a
parent class, or the "top-level type" :class:`object` if no other parent is
needed. The behaviour of new-style classes differs from that of old-style
classes in a number of important details in addition to what :func:`type`
returns. Some of these changes are fundamental to the new object model, like
the way special methods are invoked. Others are "fixes" that could not be
implemented before for compatibility concerns, like the method resolution order
in case of multiple inheritance.
This manual is not up-to-date with respect to new-style classes. For now,
please see http://www.python.org/doc/newstyle/ for more information.
.. XXX remove old style classes from docs
.. _specialnames:
Special method names
@ -1418,9 +1379,7 @@ continuing through the base classes of ``type(a)`` excluding metaclasses.
However, 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 and how they were called. Note that descriptors
are only invoked for new style objects or classes (ones that subclass
:class:`object()` or :class:`type()`).
descriptor methods were defined and how they were called.
The starting point for descriptor invocation is a binding, ``a.x``. How the
arguments are assembled depends on ``a``:
@ -1477,7 +1436,7 @@ saved because *__dict__* is not created for each instance.
.. data:: object.__slots__
This class variable can be assigned a string, iterable, or sequence of
strings with variable names used by instances. If defined in a new-style
strings with variable names used by instances. If defined in a
class, *__slots__* reserves space for the declared variables and prevents the
automatic creation of *__dict__* and *__weakref__* for each instance.
@ -1801,7 +1760,7 @@ left undefined.
``-``, ``*``, ``/``, ``%``, :func:`divmod`, :func:`pow`, ``**``, ``<<``, ``>>``,
``&``, ``^``, ``|``) with reflected (swapped) operands. These functions are
only called if the left operand does not support the corresponding operation and
the operands are of different types. [#]_ For instance, to evaluate the
the operands are of different types. [#]_ For instance, to evaluate the
expression *x*``-``*y*, where *y* is an instance of a class that has an
:meth:`__rsub__` method, ``y.__rsub__(x)`` is called if ``x.__sub__(y)`` returns
*NotImplemented*.
@ -1927,18 +1886,6 @@ For more information on context managers, see :ref:`typecontextmanager`.
.. rubric:: Footnotes
.. [#] Since Python 2.2, a gradual merging of types and classes has been started that
makes this and a few other assertions made in this manual not 100% accurate and
complete: for example, it *is* now possible in some cases to change an object's
type, under certain controlled conditions. Until this manual undergoes
extensive revision, it must now be taken as authoritative only regarding
"classic classes", that are still the default, for compatibility purposes, in
Python 2.2 and 2.3. For more information, see
http://www.python.org/doc/newstyle/.
.. [#] This, and other statements, are only roughly true for instances of new-style
classes.
.. [#] A descriptor can define any combination of :meth:`__get__`,
:meth:`__set__` and :meth:`__delete__`. If it does not define :meth:`__get__`,
then accessing the attribute even on an instance will return the descriptor
@ -1949,4 +1896,3 @@ For more information on context managers, see :ref:`typecontextmanager`.
.. [#] For operands of the same type, it is assumed that if the non-reflected method
(such as :meth:`__add__`) fails the operation is not supported, which is why the
reflected method is not called.