gh-136880: Add warning about PYTHONPATH (GH-151098)

diff --git a/Doc/tutorial/venv.rst b/Doc/tutorial/venv.rst
index f362e1943b666f7b053bed08a1bb4a1df9851f83..6b6b8a768e3f58d0218d0dde2592b91c0997d96d 100644 (file)
--- a/Doc/tutorial/venv.rst
+++ b/Doc/tutorial/venv.rst
@@ -88,6 +88,11 @@ For example:
   '~/envs/tutorial-env/lib/python3.5/site-packages']
   >>>
 
+Note that the activated virtual environment does not alter the ``PYTHONPATH`` variable in any way.
+This may lead to unexpected results if the path includes references to code which is incompatible with
+the Python version the virtual environment is using. The best practice is to ``unset PYTHONPATH``
+in bash or the equivalent for the shell you are using.
+
 To deactivate a virtual environment, type::
 
     deactivate