Monitor autoconfiguration script

mon.py

#!/usr/bin/env python3
"""
CLI script for setting display modes through xrandr.
"""
from argparse import ArgumentParser
from collections import OrderedDict
import re
from subprocess import call, Popen, PIPE
from shlex import quote
from time import sleep

import pyudev

DISPLAYS = [
    "HDMI2",
    "eDP1",
    "DP1"
]

MODES = {
    "nb": {
        "eDP1": ["--auto"]
    },
    "1ext": {
        "eDP1": ["--auto"],
        "HDMI2": ["--auto", "--left-of", "eDP1"]
    },
    "ext": {
        "DP1": ["--auto"],
        "HDMI2": ["--auto", "--left-of", "DP1"]
    },
}

AUTO = {
    "eDP1": "nb",
    "HDMI2, eDP1": "1ext",
    "DP1, HDMI2, eDP1": "ext",
}

def get_displays():
    """
    Lists the names of the currently-connected displays
    """
    proc = Popen(['xrandr', '-q'], stdout=PIPE)
    output = proc.communicate()[0].decode(errors='replace')
    connected_re = re.compile("^([a-zA-Z0-9]+) connected ")
    connected = []

    for line in output.split('\n'):
        match = connected_re.match(line)
        if match is None:
            continue
        connected.append(match.groups()[0])
        yield connected[-1]


def get_automatic_mode():
    """
    Returns the suitable mode for the currently-connected displays
    """
    displays = ", ".join(sorted(get_displays()))
    print("connected displays: " + displays)
    result = AUTO.get(displays)
    print("automatic mode: %r" % result)
    return result


def configure_displays(mode):
    """
    Configures the displays to the given mode
    """
    displays = OrderedDict()

    displays["HDMI2"] = ["--off"]
    displays["eDP1"] = ["--off"]
    displays["DP1"] = ["--off"]

    mode_info = MODES.get(mode)
    if mode_info is None:
        raise ValueError("unknown mode %r" % mode)

    invocation = ["xrandr"]
    for displayname in DISPLAYS:
        invocation.append("--output")
        invocation.append(displayname)
        invocation.extend(mode_info.get(displayname, ["--off"]))

    print(" ".join(quote(x) for x in invocation))
    call(invocation)


def main():
    """ CLI entry point """
    cli = ArgumentParser()
    cli.add_argument("mode")
    args = cli.parse_args()
    mode = args.mode

    if mode == "daemon":
        context = pyudev.Context()
        udev_monitor = pyudev.Monitor.from_netlink(context)
        udev_monitor.filter_by(subsystem='drm')

        while True:
            try:
                configure_displays(get_automatic_mode())
            except ValueError as exc:
                print(exc)

            # wait for next udev hotplug event
            hotplug_device = udev_monitor.poll()
            if hotplug_device is None:
                return
            print("hotplug: %r" % hotplug_device)
            sleep(0.5)
    else:
        # run once
        if mode == "auto":
            mode = get_automatic_mode()

        try:
            configure_displays(mode)
        except ValueError as exc:
            cli.error(str(exc))

if __name__ == '__main__':
    main()