Reimplements the :meth:`QLabel.mouseReleaseEvent` method.

        :param event: QEvent.
        :type event: QEvent

def mouseReleaseEvent(self, event):
        """
        Reimplements the :meth:`QLabel.mouseReleaseEvent` method.

        :param event: QEvent.
        :type event: QEvent
        """

        if self.underMouse():
            if self.__checkable:
                self.set_checked(not self.__checked)
            else:
                self.setPixmap(self.__active_pixmap)
        else:
            self.setPixmap(self.__default_pixmap)
        self.released.emit()
        self.clicked.emit()