Author: raymond.hettinger Date: Sun Oct 31 23:39:33 2010 New Revision: 86074 Log: Issue #9886: Add a key-function entry to the glossary. Modified: python/branches/release31-maint/Doc/glossary.rst Modified: python/branches/release31-maint/Doc/glossary.rst ============================================================================== --- python/branches/release31-maint/Doc/glossary.rst (original) +++ python/branches/release31-maint/Doc/glossary.rst Sun Oct 31 23:39:33 2010 @@ -283,6 +283,26 @@ 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