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| -rw-r--r-- | Doc/glossary.rst | 20 | ||||
| -rw-r--r-- | Doc/howto/sorting.rst | 2 |
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diff --git a/Doc/glossary.rst b/Doc/glossary.rst index 707091841b..24bbb378ea 100644 --- a/Doc/glossary.rst +++ b/Doc/glossary.rst @@ -362,6 +362,26 @@ Glossary value is assigned. ``**`` is used to accept or pass a dictionary of keyword arguments. See :term:`argument`. + 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-howto` for + examples of how to create and use key functions. + lambda An anonymous inline function consisting of a single :term:`expression` which is evaluated when the function is called. The syntax to create diff --git a/Doc/howto/sorting.rst b/Doc/howto/sorting.rst index 79008a7322..5acd405ff0 100644 --- a/Doc/howto/sorting.rst +++ b/Doc/howto/sorting.rst @@ -1,3 +1,5 @@ +.. _sorting-howto: + Sorting HOW TO ************** |