bpo-35712: Make using NotImplemented in a boolean context issue a deprecation warning (GH-13195)

1 files changed, 7 insertions, 2 deletions

diff --git a/Doc/reference/datamodel.rst b/Doc/reference/datamodel.rst
index 5b3b669..8be432d 100644
--- a/Doc/reference/datamodel.rst
+++ b/Doc/reference/datamodel.rst
@@ -156,13 +156,18 @@ NotImplemented
    object is accessed through the built-in name ``NotImplemented``. Numeric methods
    and rich comparison methods should return this value if they do not implement the
    operation for the operands provided.  (The interpreter will then try the
-   reflected operation, or some other fallback, depending on the operator.)  Its
-   truth value is true.
+   reflected operation, or some other fallback, depending on the operator.)  It
+   should not be evaluated in a boolean context.
 
    See
    :ref:`implementing-the-arithmetic-operations`
    for more details.
 
+   .. versionchanged:: 3.9
+      Evaluating ``NotImplemented`` in a boolean context is deprecated. While
+      it currently evaluates as true, it will emit a :exc:`DeprecationWarning`.
+      It will raise a :exc:`TypeError` in a future version of Python.
+
 
 Ellipsis
    .. index::