Derived from https://gist.github.com/PotatoesMaster/8038613, with small changes (such as porting to Python 3 and respecting TERMCMD, if set). Useful for things like making Deluge open ranger when you click "Open Download Folder".

fdfmdaemon.py

#!/usr/bin/env python

# This program is free software. It comes without any warranty, to the extent
# permitted by applicable law. You can redistribute it and/or modify it under
# the terms of the Do What The Fuck You Want To Public License, Version 2, as
# published by Sam Hocevar. See http://www.wtfpl.net/ for more details.

"""
This is a simple daemon implementing freedesktop.org's file manager interface
(http://www.freedesktop.org/wiki/Specifications/file-manager-interface/).
"""

from gi.repository import GLib

import dbus
import dbus.service
import dbus.mainloop.glib

import os
from subprocess import Popen

def open_file_manager(uri, select=False):
    termcmd = os.environ.get('TERMCMD') or 'kitty'
    args = [termcmd, '-e', 'ranger']

    if select:
        args.append('--select')

    path = str(uri)
    if path.startswith('file://'):
        path = path[7:]
    args.append(path)

    if os.fork() == 0:
        Popen(args)
        os._exit(0)
    else:
        os.wait()

class FmObject(dbus.service.Object):

    @dbus.service.method("org.freedesktop.FileManager1",
                         in_signature='ass', out_signature='')
    def ShowFolders(self, uris, startupId):
        open_file_manager(uris[0])

    @dbus.service.method("org.freedesktop.FileManager1",
                         in_signature='ass', out_signature='')
    def ShowItems(self, uris, startupId):
        open_file_manager(uris[0], select=True)

    @dbus.service.method("org.freedesktop.FileManager1",
                         in_signature='ass', out_signature='')
    def ShowItemProperties(self, uris, startupId):
        open_file_manager(uris[0], select=True)

    @dbus.service.method("org.freedesktop.FileManager1",
                         in_signature='', out_signature='')
    def Exit(self):
        mainloop.quit()

if __name__ == '__main__':
    dbus.mainloop.glib.DBusGMainLoop(set_as_default=True)

    session_bus = dbus.SessionBus()
    name = dbus.service.BusName("org.freedesktop.FileManager1", session_bus)
    object = FmObject(session_bus, '/org/freedesktop/FileManager1')

    mainloop = GLib.MainLoop()
    mainloop.run()