From 77f5fc107e3d7de8c1e84b260bf54aeab668ea8d Mon Sep 17 00:00:00 2001
From: Georg Brandl <georg@python.org>
Date: Sat, 19 Nov 2022 07:46:35 +0100
Subject: [PATCH] guide: better document negative index behavior w.r.t.
 PySequence

Fixes #2601
---
 guide/src/class/protocols.md | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/guide/src/class/protocols.md b/guide/src/class/protocols.md
index ea3b980d..7fbd0aac 100644
--- a/guide/src/class/protocols.md
+++ b/guide/src/class/protocols.md
@@ -243,18 +243,25 @@ Use the `#[pyclass(sequence)]` annotation to instruct PyO3 to fill the `sq_lengt
 
     Implements retrieval of the `self[a]` element.
 
-    *Note:* Negative integer indexes are not handled specially.
+    *Note:* Negative integer indexes are not handled specially by PyO3.
+    However, for classes with `#[pyclass(sequence)]`, when a negative index is
+    accessed via `PySequence::get_item`, the underlying C API already adjusts
+    the index to be positive.
 
   - `__setitem__(<self>, object, object) -> ()`
 
     Implements assignment to the `self[a]` element.
     Should only be implemented if elements can be replaced.
 
+    Same behavior regarding negative indices as for `__getitem__`.
+
   - `__delitem__(<self>, object) -> ()`
 
     Implements deletion of the `self[a]` element.
     Should only be implemented if elements can be deleted.
 
+    Same behavior regarding negative indices as for `__getitem__`.
+
   * `fn __concat__(&self, other: impl FromPyObject) -> PyResult<impl ToPyObject>`
 
     Concatenates two sequences.