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:mod:`UserDict` --- Class wrapper for dictionary objects
========================================================
.. module:: UserDict
:synopsis: Class wrapper for dictionary objects.
The module defines a mixin, :class:`DictMixin`, defining all dictionary methods
for classes that already have a minimum mapping interface. This greatly
simplifies writing classes that need to be substitutable for dictionaries (such
as the shelve module).
This also module defines a class, :class:`UserDict`, that acts as a wrapper
around dictionary objects. The need for this class has been largely supplanted
by the ability to subclass directly from :class:`dict` (a feature that became
available starting with Python version 2.2). Prior to the introduction of
:class:`dict`, the :class:`UserDict` class was used to create dictionary-like
sub-classes that obtained new behaviors by overriding existing methods or adding
new ones.
The :mod:`UserDict` module defines the :class:`UserDict` class and
:class:`DictMixin`:
.. class:: UserDict([initialdata])
Class that simulates a dictionary. The instance's contents are kept in a
regular dictionary, which is accessible via the :attr:`data` attribute of
:class:`UserDict` instances. If *initialdata* is provided, :attr:`data` is
initialized with its contents; note that a reference to *initialdata* will not
be kept, allowing it be used for other purposes.
.. note::
For backward compatibility, instances of :class:`UserDict` are not
iterable.
.. class:: IterableUserDict([initialdata])
Subclass of :class:`UserDict` that supports direct iteration (e.g. ``for key in
myDict``).
In addition to supporting the methods and operations of mappings (see section
:ref:`typesmapping`), :class:`UserDict` and :class:`IterableUserDict` instances
provide the following attribute:
.. attribute:: IterableUserDict.data
A real dictionary used to store the contents of the :class:`UserDict` class.
.. class:: DictMixin()
Mixin defining all dictionary methods for classes that already have a minimum
dictionary interface including :meth:`__getitem__`, :meth:`__setitem__`,
:meth:`__delitem__`, and :meth:`keys`.
This mixin should be used as a superclass. Adding each of the above methods
adds progressively more functionality. For instance, defining all but
:meth:`__delitem__` will preclude only :meth:`pop` and :meth:`popitem` from the
full interface.
In addition to the four base methods, progressively more efficiency comes
with defining :meth:`__contains__` and :meth:`__iter__`.
Since the mixin has no knowledge of the subclass constructor, it does not define
:meth:`__init__` or :meth:`copy`.
:mod:`UserList` --- Class wrapper for list objects
==================================================
.. module:: UserList
:synopsis: Class wrapper for list objects.
.. note::
This module is available for backward compatibility only. If you are writing
code that does not need to work with versions of Python earlier than Python 2.2,
please consider subclassing directly from the built-in :class:`list` type.
This module defines a class that acts as a wrapper around list objects. It is a
useful base class for your own list-like classes, which can inherit from them
and override existing methods or add new ones. In this way one can add new
behaviors to lists.
The :mod:`UserList` module defines the :class:`UserList` class:
.. class:: UserList([list])
Class that simulates a list. The instance's contents are kept in a regular
list, which is accessible via the :attr:`data` attribute of
:class:`UserList`
instances. The instance's contents are initially set to a copy of *list*,
defaulting to the empty list ``[]``. *list* can be any iterable, for
example a real Python list or a :class:`UserList` object.
In addition to supporting the methods and operations of mutable sequences (see
section :ref:`typesseq`), :class:`UserList` instances provide the following
attribute:
.. attribute:: UserList.data
A real Python list object used to store the contents of the :class:`UserList`
class.
**Subclassing requirements:** Subclasses of :class:`UserList` are expect to
offer a constructor which can be called with either no arguments or one
argument. List operations which return a new sequence attempt to create an
instance of the actual implementation class. To do so, it assumes that the
constructor can be called with a single parameter, which is a sequence object
used as a data source.
If a derived class does not wish to comply with this requirement, all of the
special methods supported by this class will need to be overridden; please
consult the sources for information about the methods which need to be provided
in that case.
:mod:`UserString` --- Class wrapper for string objects
======================================================
.. module:: UserString
:synopsis: Class wrapper for string objects.
.. moduleauthor:: Peter Funk <pf@artcom-gmbh.de>
.. sectionauthor:: Peter Funk <pf@artcom-gmbh.de>
.. note::
This :class:`UserString` class from this module is available for backward
compatibility only. If you are writing code that does not need to work with
versions of Python earlier than Python 2.2, please consider subclassing directly
from the built-in :class:`str` type instead of using :class:`UserString` (there
is no built-in equivalent to :class:`MutableString`).
This module defines a class that acts as a wrapper around string objects. It is
a useful base class for your own string-like classes, which can inherit from
them and override existing methods or add new ones. In this way one can add new
behaviors to strings.
It should be noted that these classes are highly inefficient compared to real
string or Unicode objects; this is especially the case for
:class:`MutableString`.
The :mod:`UserString` module defines the following classes:
.. class:: UserString([sequence])
Class that simulates a string or a Unicode string object. The instance's
content is kept in a regular string or Unicode string object, which is
accessible via the :attr:`data` attribute of :class:`UserString` instances. The
instance's contents are initially set to a copy of *sequence*. *sequence* can
be either a regular Python string or Unicode string, an instance of
:class:`UserString` (or a subclass) or an arbitrary sequence which can be
converted into a string using the built-in :func:`str` function.
.. class:: MutableString([sequence])
This class is derived from the :class:`UserString` above and redefines strings
to be *mutable*. Mutable strings can't be used as dictionary keys, because
dictionaries require *immutable* objects as keys. The main intention of this
class is to serve as an educational example for inheritance and necessity to
remove (override) the :meth:`__hash__` method in order to trap attempts to use a
mutable object as dictionary key, which would be otherwise very error prone and
hard to track down.
In addition to supporting the methods and operations of string and Unicode
objects (see section :ref:`string-methods`), :class:`UserString` instances
provide the following attribute:
.. attribute:: MutableString.data
A real Python string or Unicode object used to store the content of the
:class:`UserString` class.
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