bpo-42086: Document AST operator nodes acts as a singleton (GH-22896)
Automerge-Triggered-By: GH:gvanrossum
diff --git a/Doc/library/ast.rst b/Doc/library/ast.rst
index f95ee1d..b8688ae 100644
--- a/Doc/library/ast.rst
+++ b/Doc/library/ast.rst
@@ -1503,6 +1503,13 @@
fields as :class:`For` and :class:`With`, respectively. Only valid in the
body of an :class:`AsyncFunctionDef`.
+.. note::
+ When a string is parsed by :func:`ast.parse`, operator nodes (subclasses
+ of :class:`ast.operator`, :class:`ast.unaryop`, :class:`ast.cmpop`,
+ :class:`ast.boolop` and :class:`ast.expr_context`) on the returned tree
+ will be singletons. Changes to one will be reflected in all other
+ occurrences of the same value (e.g. :class:`ast.Add`).
+
:mod:`ast` Helpers
------------------