Python: Why does this non-blocking call to recv block?

I have the following code in the $init call of a thread:

self.conn = copy.deepcopy(conn)
self.conn.setblocking(0)

conn is a socket and is passed as an argument to $init Every thread recieves a unique socket. In the run method I have:

self.running = True
self.conn.send("Connected")
print self.name, "has 开发者_StackOverflowa timeout of", self.conn.gettimeout()

while self.running:
    try:
        now = self.conn.recv(8192)
        print "Recieved:", now, "\n\tFrom:", self.name
        self.process(now)
    except socket.error:
         raise

     print "hi from", self.name
     time.sleep(1)

The timeout is printed as 0.0, but "hi from threadname" only printed out when a message is recieved and the exception is never raised! It looks as if the recv method blocks, but why would it do that?

---

Propably because recv is reading from file and I/O is blocking? (sockets are files too as you may know) :)

Look here: python socket.recv/sendall call blocking for more info :)