Multithreaded Github Username Checker

This script checks whether a username is available or not (username could be a user or an organization)
It generates multiple HTTP GET requests using a ThreadPoolExecutor and checks their response status code.
- If the status code is 404 then the username doesn't exist yet.
We use a ThreadPoolExecutor which uses a pool of threads to execute calls asynchronously.
ThreadPoolExecutor is part of the concurrent.futures module which provides a high-level interface for asynchronously executing callables.

Note:

This script can be used to check the availability of usernames for any website, I just used Github as an example.
In the case where the website doesn't respond with a 404 status code then you can still check the response content to see if it contains words like "404", "Does not exist" ...