Empty dictionaries evaluate to False
in Python:
>>> dct = {}
>>> bool(dct)
False
>>> not dct
True
>>>
Thus, your isEmpty
function is unnecessary. All you need to do is:
def onMessage(self, socket, message):
if not self.users:
socket.send("Nobody is online, please use REGISTER command" \
" in order to register into the server")
else:
socket.send("ONLINE " + ' ' .join(self.users.keys()))