Kill Python thread running a web server

I'm trying to reboot a web server written in Python during some integration testing. The server runs as a thread during the tests, so I can continue sending POST \ GET requests to it, and asserting the answers.

I tried killing the thread by force:

t._tstate_lock = None
t._stop()
t.join()

While debugging, I can actually see that the thread is stopped, but the webserver is still up, for some reason.

Any ideas?