Read from keyboard non blocking mode because of sockets working, python

Question

Im programming a client-server in python, and them when working are sending keepalive packets every second.

I need the client to read from my keyboard an action to send a special packet to the server, but when reading I can't stop sending keepalive packets, so if I read by standard way, it blocks and stops the keepalive packet sending.

The perfect behaviour would be to write in console while keepaliving, and when pressing "enter" process that text.

Any ideas please?

Thanks!

Answer 1

Found it, using select.select I could do that, like this:

selectList = [sktTCP,sys.stdin]
(read, write, exc) =  select.select(selectList, [], [], 0 )

I hope it'll help someone!

Answer 2

This is a threading issue basically. I would suggest looking into managing your network connections using Twisted. It can work asynchronously, leaving you able to pick up key presses.

Answer 3

Another way to read user input on Unix without blocking (for too long) is to use an alarm:

from signal import SIGALRM, alarm, signal

class Alarm(Exception):
    pass

def alarm_handler(*args):
    raise Alarm

def raw_input_alarm(prompt='', timeout=None):
    if timeout is None: # no timeout
        return raw_input(prompt)

    # set signal handler
    signal(SIGALRM, alarm_handler)
    alarm(timeout) # produce SIGALRM in `timeout` seconds
    try:
        return raw_input(prompt)
    except Alarm:
        return '' # timeout happened
    finally:
        alarm(0) # cancel alarm

Example

print(repr(raw_input_alarm(timeout=1)))

alarm expects integer number of seconds. If you want smaller timeout; see signal.setitimer().