Python server "Only one usage of each socket address is normally permitted"

Enable the SO_REUSEADDR socket option before calling bind(). This allows the address/port to be reused immediately instead of it being stuck in the TIME_WAIT state for several minutes, waiting for late packets to arrive.

s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)

In the article posted by @JohnKugelman it is stated that even after enabling SO_REUSEADDR you cannot use the socket to connect to the same remote end as before:

SO_REUSADDR permits you to use a port that is stuck in TIME_WAIT, but you still can not use that port to establish a connection to the last place it connected to.

I see that you are just testing/playing around. However, to avoid this error you really need to make sure that you terminate the connection properly. You could also mess with the tcp timings of the operating system: http://www.linuxquestions.org/questions/linux-networking-3/decrease-time_wait-558399/

For testing purposes it would also be fine if you just change your serverPort in a round-robin fashion, what do you think?

On Windows, you can try these steps:

1. check which process uses the port.

# 4444 is your port number
netstat -ano|findstr 4444

you will get something like this:

# 19088 is the PID of the process
TCP    0.0.0.0:4444           *:*                                    19088

2. kill this process

With:

tskill 19088

Or:

taskkill /F /PID 19088

Good luck.