[3.10] bpo-45246: Document that sorted() only uses "<" comparisons (GH-28494) (GH-28502)
(cherry picked from commit 9a0dcc5b2e04d9c51350107734f12a1cbc0284a7)
Co-authored-by: Raymond Hettinger <rhettinger@users.noreply.github.com>
diff --git a/Doc/library/functions.rst b/Doc/library/functions.rst
index 9629ace..e89323f 100644
--- a/Doc/library/functions.rst
+++ b/Doc/library/functions.rst
@@ -1603,6 +1603,15 @@
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
+ <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