: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:
+ the :mod:`operator` module provides three key function constructors:
:func:`~operator.attrgetter`, :func:`~operator.itemgetter`, and
:func:`~operator.methodcaller`. See the :ref:`Sorting HOW TO
<sortinghowto>` for examples of how to create and use key functions.