Python3 example to use Gio and GLib to run subprocesses and asynchronously read stdout/stderr

gio_subprocess.py

#!/usr/bin/env python3
from gi.repository import Gio, GLib
import shlex
import signal

priority = GLib.PRIORITY_DEFAULT


class ProcessLauncher:
    def run(self, cmd):
        self.cancellable = Gio.Cancellable()
        try:
            flags = Gio.SubprocessFlags.STDOUT_PIPE | Gio.SubprocessFlags.STDERR_MERGE
            args = shlex.split(cmd)
            self.process = p = Gio.Subprocess.new(args, flags)
            p.wait_check_async(
                cancellable=self.cancellable,
                callback=self._on_finished
            )
            print('Started')
            stream = p.get_stdout_pipe()
            self.data_stream = Gio.DataInputStream.new(stream)
            self.queue_read()
        except GLib.GError as e:
            print(e)

    def queue_read(self):
        self.data_stream.read_line_async(
            io_priority=priority,
            cancellable=self.cancellable,
            callback=self._on_data
        )

    def cancel_read(self):
        print('Cancelling read')
        self.cancellable.cancel()

    def _on_finished(self, proc, results):
        print('Process finished')
        try:
            proc.wait_check_finish(results)
        except Exception as e:
            print(e)
        self.cancel_read()

    def _on_data(self, source, result):
        try:
            line, length = source.read_line_finish_utf8(result)
            if line:
                print(line)
        except GLib.GError as e:
            print(e)
            return
        self.queue_read()

    def stop(self):
        print('Stop')
        self.process.send_signal(signal.SIGTERM)

    def kill(self):
        print('Kill')
        self.cancel_read()
        self.process.send_signal(signal.SIGKILL)


if __name__ == '__main__':
    p = ProcessLauncher()
    m = GLib.MainLoop()
    GLib.idle_add(p.run, "/usr/bin/journalctl -f")
    GLib.timeout_add_seconds(priority=priority, interval=5, function=p.stop)
    m.run()

TBH i just found it somewhere and stored it exactly for the same reason. Thanks for the investigation !