I have a python server that listens on a couple sockets. At startup, I try to connect to these sockets before listening, so I can be sure that nothing else is already using that port. This adds about three seconds to my server's startup (which is about .54 seconds without the test) and I'd like to trim it down. Since I'm only testing localhost, I think a timeout of about 50 milliseconds is more than ample for that. Unfortunately, the socket.setdefaulttimeout(50) method doesn't seem to work for some reason.
How I can trim this down?
How about just trying to bind to the port you want, and handle the error case if the port is occupied? (If the issue is that you might start the same service twice then don't look at open ports.)
This is the reasonable way also to avoid causing a race-condition, as @eemz said in another answer.