TO run the chat first have to run the server file:

$ sudo su $ cd /folder name/ $ python chatserver.py

after you share the communication.py and chatclient.py files with friends or copy to other machine have to run

$ sudo su $ cd /folder name/ $ python chatclient.py localhost 3490

REMEMBER: to personalise the username you have to rename the chatclient.py file

AND don't forget to change that also when you run the client.

EX: python rename_chatclient.py localhost 3940