gistfile1.py

#!/usr/bin/python

from gi.repository import GLib, Gdk, GConf, Gio

def update_hide_mode(screen):
    form_factor_settings = Gio.Settings.new('com.canonical.Unity')
    launcher_hide_mode_settings = Gio.Settings.new_with_path('org.compiz.unityshell', '/org/compiz/profiles/unity/plugins/unityshell/')
    form_factor_key = 'form-factor'
    launcher_hide_mode_key = 'launcher-hide-mode'
    size = min(screen.get_monitor_geometry(i).width for i in xrange(screen.get_n_monitors()))
    if size < 1400:
        form_factor_settings.set_enum(form_factor_key, 2)
        launcher_hide_mode_settings.set_int(launcher_hide_mode_key, 1)
    else:
        form_factor_settings.set_enum(form_factor_key, 1)
        launcher_hide_mode_settings.set_int(launcher_hide_mode_key, 0)

def main():
    s = Gdk.Screen.get_default()
    s.connect('monitors-changed', update_hide_mode)
    update_hide_mode(s)
    GLib.MainLoop().run()

if __name__ == '__main__':
    main()