foo.py

#!/usr/bin/env python2
# encoding: utf-8

import dbus, gobject, re
from dbus.mainloop.glib import DBusGMainLoop

INACTIVE_STATES = ("inactive", "failed")
UNIT_INTERFACE = 'org.freedesktop.systemd1.Unit' 

unit_regex = re.compile('[^A-Za-z0-9]')

DBusGMainLoop(set_as_default=True)

event_loop = gobject.MainLoop()
bus = dbus.SessionBus()

manager_int = dbus.Interface(
    bus.get_object('org.freedesktop.systemd1', '/org/freedesktop/systemd1'),
    dbus_interface="org.freedesktop.systemd1.Manager"
)


def wait(unit):
    path = "/org/freedesktop/systemd1/unit/" + unit_regex.sub(
        lambda x: "_" + x.group(0).encode("hex"),
        unit
    )
    unit_int = dbus.Interface(
        bus.get_object('org.freedesktop.systemd1',
                       path),
        dbus_interface=dbus.PROPERTIES_IFACE
    )

    def handler(interface, changed, invalidated):
        if interface == UNIT_INTERFACE \
           and "ActiveState" in invalidated \
           and unit_int.Get(interface, "ActiveState") in INACTIVE_STATES:
            event_loop.quit()

    unit_int.connect_to_signal('PropertiesChanged', handler, utf8_strings=True)

    manager_int.Subscribe()
    event_loop.run()
    manager_int.Unsubscribe()

if __name__ == '__main__':
    import sys
    if len(sys.argv) != 2:
        print "Usage: %s UNIT" % sys.argv[0]
        exit(1)
    wait(sys.argv[1])