def keyPressEvent(self, event):
        """Reimplemented."""
        # Override the default QComboBox behavior
        if event.key() == Qt.Key_Down and event.modifiers() & Qt.AltModifier:
            self.showPopup()
            return

        ignored = {Qt.Key_Up, Qt.Key_Down,
                   Qt.Key_PageDown, Qt.Key_PageUp,
                   Qt.Key_Home, Qt.Key_End}

        if event.key() in ignored:
            event.ignore()
            return

        super(CheckComboBox, self).keyPressEvent(event) 

def page_up(self, count=1):
        self._key_press(Qt.Key_PageUp, count, 'scrollBarMinimum', Qt.Vertical)