In article <b8d42424-e0ab-4595-9c87-25e5c1b53...@googlegroups.com>, Bhanu Karthik <bhanukarthik2...@gmail.com> wrote:
> please help me.. what does the following line do? > > read_sockets,write_sockets,error_sockets = > select.select(CONNECTION_LIST,[],[]) This is a little tricky. First,read the docs at http://docs.python.org/2/library/select.html. There's a lot of complicated stuff there, but just concentrate on the description of the select.select() call for now. Imagine a process which has a lot of network connections open. A great example would be something like a MUD (Multi User Dungeon). You've got one server process(*) and a bunch of clients which have all made TCP connections over individual sockets. Each client will be sending commands asynchronously, and the server needs to handle this. You need some way to figure out which of those sockets have something that's been sent to you (which you need to process) and which are just sitting idle. That's where select() comes in. It gives you a way to say, "Here's a list of sockets. Sleep until one of them has something available for me to read, and let me know which one." One bit of complication is that you can also check for sockets which are ready to be written on, and sockets which have some sort of error condition. That's why the call returns a 3-tuple. But, for now, let's just concentrate on reading. Here's a very simplistic server which uses select(): import socket import select sock = socket.socket() sock.bind(('localhost', 23000)) sock.listen(10) # Accept four connections. connections = [] for i in range(4): s, addr = sock.accept() print "Got connection from %s" % str(addr) connections.append(s) while True: readable, _, _ = select.select(connections, [], []) print "ready for reading: %s" % readable for s in readable: data = s.recv(1024) print "Read from %s: %s" % (s, data) You can write a little client which connects to this (I've got one I used for testing, but I'll leave it to you to write one yourself as an exercise). Connect four clients, and have them send some input in random order. Actually, this server has a bug (which you'll discover as soon as you close one of the four connection), but it should serve to illustrate the basic concept. (*) I'm not sure if real MUDs are programmed this way, but it's a plausible architecture. For simplicity sake, I'm assuming a single-threaded server. -- https://mail.python.org/mailman/listinfo/python-list
