diff options
Diffstat (limited to 'Doc/reference/datamodel.rst')
| -rw-r--r-- | Doc/reference/datamodel.rst | 63 |
1 files changed, 44 insertions, 19 deletions
diff --git a/Doc/reference/datamodel.rst b/Doc/reference/datamodel.rst index 49bc8b6..0ec255f 100644 --- a/Doc/reference/datamodel.rst +++ b/Doc/reference/datamodel.rst @@ -202,8 +202,6 @@ Numbers operation except left shift, if it yields a result in the plain integer domain without causing overflow, will yield the same result when using mixed operands. - .. % Integers - Floating point numbers .. index:: object: floating point @@ -229,8 +227,6 @@ Numbers The real and imaginary parts of a complex number ``z`` can be retrieved through the read-only attributes ``z.real`` and ``z.imag``. - .. % Numbers - Sequences .. index:: builtin: len @@ -302,8 +298,6 @@ Sequences parentheses must be usable for grouping of expressions). An empty tuple can be formed by an empty pair of parentheses. - .. % Immutable sequences - Mutable sequences .. index:: object: mutable sequence @@ -341,10 +335,6 @@ Sequences The extension module :mod:`array` provides an additional example of a mutable sequence type. - .. % Mutable sequences - - .. % Sequences - Set types .. index:: builtin: len @@ -379,8 +369,6 @@ Set types :term:`hashable`, it can be used again as an element of another set, or as a dictionary key. - .. % Set types - Mappings .. index:: builtin: len @@ -418,8 +406,6 @@ Mappings The extension modules :mod:`dbm`, :mod:`gdbm`, and :mod:`bsddb` provide additional examples of mapping types. - .. % Mapping types - Callable types .. index:: object: callable @@ -652,8 +638,6 @@ Modules object used to initialize the module (since it isn't needed once the initialization is done). - .. % - Attribute assignment updates the module's namespace dictionary, e.g., ``m.x = 1`` is equivalent to ``m.__dict__["x"] = 1``. @@ -992,12 +976,53 @@ Internal types described above, under "User-defined methods". Class method objects are created by the built-in :func:`classmethod` constructor. - .. % Internal types - -.. % ========================================================================= .. _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 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.html for more information. + +.. index:: + single: class + single: class + single: class + +The plan is to eventually drop old-style classes, leaving only the semantics of +new-style classes. This change will probably only be feasible in Python 3.0. +new-style classic old-style + + .. _specialnames: Special method names |