[pygtk] How can I inherit __gsignals__ attribute from a class?

[Iven Day]

Hi,
    I wrote a parent class like this:

class PluginObject(gobject.GObject):
    __gsignals__ = {
            "change-ui": (gobject.SIGNAL_RUN_FIRST,
                          gobject.TYPE_NONE,
                         (gobject.TYPE_PYOBJECT, gobject.TYPE_STRING,)),
                   }
    def __init__(self):
        gobject.GObject.__init__(self)

, and a child class like this:

class PluginComboBox(gtk.ComboBox, PluginObject):
    def __init__(self, input_dict):
        PluginObject.__init__(self)
        gtk.ComboBox.__init__(self)
        ...
        self.connect("changed", self.changed_cb, input_dict)
        self.set_active(0)
    def changed_cb(self, widget, data = None):
        model = self.get_model()
        index = self.get_active()
        self.emit("change-ui", data.values, data[model[index][0]])

, but I got a

TypeError: <PluginComboBox object at 0x7f02c4c20690 (GtkComboBox at
0x26e8010)>: unknown signal name: change-ui

It seems __gsignals__ isn't inherited, how can I get it work?
Sorry for my english.