Do not exit python program, but keep running

gtk.main() runs an event loop. It doesn't exit, and it doesn't just freeze up doing nothing, because inside it has code kind of like this:

while True:
    timeout = timers.earliest() - datetime.now()
    try:
        message = wait_for_next_gui_message(timeout)
    except TimeoutError:
        handle_any_expired_timers()
    else:
        handle_message(message)

That wait_for_next_gui_message function is a wrapper around different platform-specific functions that wait for X11, WindowServer, the unnamed thing in Windows, etc. to deliver messages like "user clicked your button" or "user hit ctrl-Q".

If you call http.serve_forever() or similar on a twisted, HTTPServer, etc., it's doing exactly the same thing, except it's a wait_for_next_network_message(sources, timeout) function, which wraps something like select.select, where sources is a list of all of your sockets.

If you're listening on a gstreamer pipe, your sources can just be that pipe, and the wait_for_next function just select.select.

Or, of course, you could use a networking framework like twisted.

However, you don't need to design your app this way. If you don't need to wait for multiple sources, you can just block:

while True:
    data = pipe.read()
    handle_data(data)

Just make sure the pipe is not set to nonblocking. If you're not sure, you can use setblocking on a socket, fcntl on a Unix pipe, or something I can't remember off the top of my head on a Windows pipe to make sure.

In fact, even if you need to wait for multiple sources, you can do this, by putting a blocking loop for each source into a separate thread (or process). This won't work for thousands of sockets (although you can use greenlets instead of threads for that case), but it's fine for 3, or 30.

I've become a fan of the Cmd class. It gives you a shell prompt for your programs and will stay in the loop while waiting for input. Here's the link to the docs. It might do what you want.