In the question Python – non-blocking sockets using selectors the following code is used: events = selectors.EVENT_READ | selectors.EVENT_WRITE The values of event_read or event_write flags are not mentioned nor explained at https://docs.python.org/3/library/selectors.html. Neither is an explanation give in the select() module or given at https://realpython.com/python-sockets/. It would be appreciated to emphasize on this particular part or provide reading material