non-blocking socket,error is always
===

    sock.setblocking(0)
    try:
        data = sock.recv(1024)
     except socket.error, e:
        if e.args[0] == errno.EWOULDBLOCK: 
              print 'EWOULDBLOCK'
              data = ''            
    if not data:   #recv over
         sock.close()
         print 'close================='       
    else:
         print 'recv ---data---------'
         poem += data
all above code is in a loop.using `non-blocking socket`(just want to test 'non-blocking socket') to get data. But always print 'EWOULDBLOCK',i don't know why? 