Writing currently playing clementine track to file

clementine_gettrack.py

#!/usr/bin/python

import dbus
import dbus.mainloop.glib
import glib

dbus.mainloop.glib.DBusGMainLoop (set_as_default = True)
session_bus = dbus.SessionBus()

def write_track(track):
    f = open( 'now_playing.txt', 'w' )
    f.write( track )
    f.close()

def get_track():
    global properties_manager
    metadata = properties_manager.Get('org.mpris.MediaPlayer2.Player', 'Metadata')
    return (metadata['xesam:artist'][0] if 'xesam:artist' in metadata else 'Unknown') + ' - ' + (metadata['xesam:title'] if 'xesam:title' in metadata else 'Unknown')

def property_changed(one,two,three):
    global properties_manager
    global track
    metadata = properties_manager.Get('org.mpris.MediaPlayer2.Player', 'Metadata')
    track2 = get_track()
    if track != track2:
        track = track2
        write_track(track)

player = session_bus.get_object('org.mpris.MediaPlayer2.clementine', '/org/mpris/MediaPlayer2')
properties_manager = dbus.Interface(player, 'org.freedesktop.DBus.Properties')
metadata = properties_manager.Get('org.mpris.MediaPlayer2.Player', 'Metadata')
track = get_track()
write_track(track)

properties_manager.connect_to_signal ("PropertiesChanged", property_changed)
mainloop = glib.MainLoop()
mainloop.run()