Core Python Programming (2nd Edition)

One way to create this "friendly" exit is to put the server's while loop
inside the except clause of a TRy-except statement and monitor for
EOFError or KeyboardInterrupt exceptions. Then in the except clause,
you can make a call to close the server's socket.
The interesting thing about this simple networked application is that we are not only showing how our
data take a round trip from the client to the server and back to the client, but we also use the server as
a sort of "time server," because the timestamp we receive is purely from the server.
16.3.6. Creating a UDP Server
UDP servers do not require as much setup as TCP servers because they are not connection-oriented.
There is virtually no work that needs to be done other than just waiting for incoming connections.
ss = socket() # create server socket
ss.bind() # bind server socket
inf_loop: # server infinite loop
cs = ss.recvfrom()/ss.sendto()# dialog (receive/send)
ss.close() # close server socket
As you can see from the pseudocode, there is nothing extra other than the usual create-the-socket and
bind it to the local address (host/port pair). The infinite loop consists of receiving a message from a
client, returning a timestamped one, then going back to wait for another message. Again, the close()
call is optional and will not be reached due to the infinite loop, but it serves as a reminder that it should
be part of the graceful or intelligent exit scheme we've been mentioning.
One other significant different between UDP and TCP servers is that because datagram sockets are
connectionless, there is no "handing off" of a client connection to a separate socket for succeeding
communication. These servers just accept messages and perhaps reply.
You will find the code to tsUserv.py in Example 16.3, a UDP version of the TCP server seen earlier. It
accepts a client message and returns it to the client timestamped.
Example 16.3. UDP Timestamp Server (tsUserv.py)