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author | Georg Brandl <georg@python.org> | 2007-08-15 14:28:22 (GMT) |
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committer | Georg Brandl <georg@python.org> | 2007-08-15 14:28:22 (GMT) |
commit | 116aa62bf54a39697e25f21d6cf6799f7faa1349 (patch) | |
tree | 8db5729518ed4ca88e26f1e26cc8695151ca3eb3 /Doc/library/userdict.rst | |
parent | 739c01d47b9118d04e5722333f0e6b4d0c8bdd9e (diff) | |
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Move the 3k reST doc tree in place.
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diff --git a/Doc/library/userdict.rst b/Doc/library/userdict.rst new file mode 100644 index 0000000..11d46ed --- /dev/null +++ b/Doc/library/userdict.rst @@ -0,0 +1,188 @@ + +: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__`, :meth:`__iter__`, and :meth:`iteritems`. + + 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, e.g. 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. + +.. versionchanged:: 2.0 + Python versions 1.5.2 and 1.6 also required that the constructor be callable + with no parameters, and offer a mutable :attr:`data` attribute. Earlier + versions of Python did not attempt to create instances of the derived class. + + +: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. + |