From aea92de9900ceb8d679a9324fc72621940b9c8a0 Mon Sep 17 00:00:00 2001 From: "Miss Islington (bot)" <31488909+miss-islington@users.noreply.github.com> Date: Tue, 21 Sep 2021 10:53:26 -0700 Subject: [PATCH] bpo-45246: Document that sorted() only uses "<" comparisons (GH-28494) (cherry picked from commit 9a0dcc5b2e04d9c51350107734f12a1cbc0284a7) Co-authored-by: Raymond Hettinger --- Doc/library/functions.rst | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/Doc/library/functions.rst b/Doc/library/functions.rst index 39ce338d3887..15bfbf40462f 100644 --- a/Doc/library/functions.rst +++ b/Doc/library/functions.rst @@ -1547,6 +1547,15 @@ are always available. They are listed here in alphabetical order. compare equal --- this is helpful for sorting in multiple passes (for example, sort by department, then by salary grade). + The sort algorithm uses only ``<`` comparisons between items. While + defining an :meth:`~object.__lt__` method will suffice for sorting, + :PEP:`8` recommends that all six :ref:`rich comparisons + ` be implemented. This will help avoid bugs when using + the same data with other ordering tools such as :func:`max` that rely + on a different underlying method. Implementing all six comparisons + also helps avoid confusion for mixed type comparisons which can call + reflected the :meth:`~object.__gt__` method. + For sorting examples and a brief sorting tutorial, see :ref:`sortinghowto`. .. decorator:: staticmethod -- 2.47.3