getnotify() method tries to get a notify from the server (from the SQL statement NOTIFY). If the server returns no notify, the methods returns None. Otherwise, it returns a tuple (couple) (relname, pid), where relname is the name of the notify and pid the process id of the connection that triggered the notify. Remember to do a listen query first otherwise getnotify will always return None.
If you see anything in the documentation that is not correct, does not match your experience with the particular feature or requires further clarification, please use this form to report a documentation issue.