[Python-checkins] r86073 - python/branches/py3k/Doc/glossary.rst
raymond.hettinger
python-checkins at python.org
Sun Oct 31 23:36:07 CET 2010
Author: raymond.hettinger
Date: Sun Oct 31 23:36:06 2010
New Revision: 86073
Log:
Issue #9886: Add a key-function entry to the glossary.
Modified:
python/branches/py3k/Doc/glossary.rst
Modified: python/branches/py3k/Doc/glossary.rst
==============================================================================
--- python/branches/py3k/Doc/glossary.rst (original)
+++ python/branches/py3k/Doc/glossary.rst Sun Oct 31 23:36:06 2010
@@ -288,6 +288,26 @@
instances of user-defined classes are hashable by default; they all
compare unequal, and their hash value is their :func:`id`.
+ key function
+ A key function or collation function is a callable that returns a value
+ used for sorting or ordering. For example, :func:`locale.strxfrm` is
+ used to produce a sort key that is aware of locale specific sort
+ conventions.
+
+ A number of tools in Python accept key functions to control how elements
+ are ordered or grouped. They include :func:`min`, :func:`max`,
+ :func:`sorted`, :meth:`list.sort`, :func:`heapq.nsmallest`,
+ :func:`heapq.nlargest`, and :func:`itertools.groupby`.
+
+ There are several ways to create a key function. For example. the
+ :meth:`str.lower` method can serve as a key function for case insensitive
+ sorts. Alternatively, an ad-hoc key function can be built from a
+ :keyword:`lambda` expression such as ``lambda r: (r[0], r[2])``. Also,
+ the :mod:`operator` module provides three key function constuctors:
+ :func:`~operator.attrgetter`, :func:`~operator.itemgetter`, and
+ :func:`~operator.methodcaller`. See the :ref:`Sorting HOW TO` for
+ examples of how to create and use key functions.
+
IDLE
An Integrated Development Environment for Python. IDLE is a basic editor
and interpreter environment which ships with the standard distribution of
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