If the gconf var use_default_font be changed, this method
        will be called and will change the font style to the gnome
        default or to the chosen font in style/font/style in all
        terminals open.

def default_font_toggled(self, settings, key, user_data):
        """If the gconf var use_default_font be changed, this method
        will be called and will change the font style to the gnome
        default or to the chosen font in style/font/style in all
        terminals open.
        """
        font_name = None
        if settings.get_boolean(key):
            gio_settings = Gio.Settings('org.gnome.desktop.interface')
            font_name = gio_settings.get_string('monospace-font-name')
        else:
            font_name = self.settings.styleFont.get_string('style')
        if not font_name:
            log.error("Error: unable to find font name (%s)", font_name)
            return
        font = Pango.FontDescription(font_name)
        if not font:
            log.error("Error: unable to load font (%s)", font_name)
            return
        for i in self.guake.notebook_manager.iter_terminals():
            i.set_font(font)