From 009ef2955d91e04f62a7159a1c7ddaddbfedc3b6 Mon Sep 17 00:00:00 2001
From: Jeroen Demeyer <J.Demeyer@UGent.be>
Date: Tue, 10 Sep 2019 16:01:13 +0200
Subject: [PATCH] bpo-37913: document that __length_hint__ can return
NotImplemented (GH-15383)
---
Doc/reference/datamodel.rst | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/Doc/reference/datamodel.rst b/Doc/reference/datamodel.rst
index 8813f57587..6b9325da2f 100644
--- a/Doc/reference/datamodel.rst
+++ b/Doc/reference/datamodel.rst
@@ -2155,8 +2155,10 @@ through the container; for mappings, :meth:`__iter__` should be the same as
Called to implement :func:`operator.length_hint`. Should return an estimated
length for the object (which may be greater or less than the actual length).
- The length must be an integer ``>=`` 0. This method is purely an
- optimization and is never required for correctness.
+ The length must be an integer ``>=`` 0. The return value may also be
+ *NotImplemented*, which is treated the same as if the ``__length_hint__``
+ method didn't exist at all. This method is purely an optimization and is
+ never required for correctness.
.. versionadded:: 3.4
--
2.50.0