Кнопка переключения в PyQt

Я реализовал следующую кнопку-переключатель в PyQt4, но не могу понять, почему она ведет себя не так, как ожидалось, когда находится в состоянии «ВЫКЛ». Я не могу понять, в чем проблема. Любая помощь будет ценна и высоко оценена.

При этом вы можете найти мой код прикрепленным.

from PyQt4.QtCore import QObject
from PyQt4.QtGui import QPen
from PyQt4.QtGui import QBrush
from PyQt4.QtGui import QPalette
from PyQt4.QtGui import QAbstractButton
from PyQt4.QtGui import QPainter
from PyQt4.QtGui import QApplication
from PyQt4.QtCore import QRectF
from PyQt4.QtGui import QLinearGradient, QGradient
from PyQt4.QtCore import QPropertyAnimation
from PyQt4.QtCore import QEasingCurve
from PyQt4.QtCore import Qt, QSize
from PyQt4.QtCore import pyqtProperty, pyqtSlot


class QSlideSwitchPrivate(QObject):

    def __init__(self, q):
        QObject.__init__(self)

        self._position = 0
        self._sliderShape = QRectF()
        self._gradient = QLinearGradient()
        self._gradient.setSpread(QGradient.PadSpread)
        self._qPointer = q

        self.animation = QPropertyAnimation(self)
        self.animation.setTargetObject(self)
        self.animation.setPropertyName("position")
        self.animation.setStartValue(0)
        self.animation.setEndValue(1)
        self.animation.setDuration(300)
        self.animation.setEasingCurve(QEasingCurve.InOutExpo)

    def __del__(self):
        del self.animation

    @pyqtProperty(float)
    def position(self):
        return self._position

    @position.setter
    def position(self, value):
        self._position = value
        self._qPointer.repaint()

    def drawSlider(self, painter):
        margin = 3
        r = self._qPointer.rect().adjusted(0,0,-1,-1)
        dx = (r.width() - self._sliderShape.width()) * self._position
        sliderRect = self._sliderShape.translated(dx, 0)
        painter.setPen(Qt.NoPen)

        # basic settings
        shadow = self._qPointer.palette().color(QPalette.Dark)
        light = self._qPointer.palette().color(QPalette.Light)
        button = self._qPointer.palette().color(QPalette.Button)

        # draw background
        # draw outer background
        self._gradient.setColorAt(0, shadow.darker(130))
        self._gradient.setColorAt(1, light.darker(130))
        self._gradient.setStart(0, r.height())
        self._gradient.setFinalStop(0, 0)
        painter.setBrush(self._gradient)
        painter.drawRoundedRect(r, 15, 15)

        # draw background
        # draw inner background
        self._gradient.setColorAt(0, shadow.darker(140))
        self._gradient.setColorAt(1, light.darker(160))
        self._gradient.setStart(0, 0)
        self._gradient.setFinalStop(0, r.height())
        painter.setBrush(self._gradient)
        painter.drawRoundedRect(r.adjusted(margin, margin, -margin, -margin), 15, 15)

        # draw slider
        self._gradient.setColorAt(0, button.darker(130))
        self._gradient.setColorAt(1, button)

        # draw outer slider
        self._gradient.setStart(0, r.height())
        self._gradient.setFinalStop(0, 0)
        painter.setBrush(self._gradient)
        painter.drawRoundedRect(sliderRect.adjusted(margin, margin, -margin, -margin), 10, 15)

        # draw inner slider
        self._gradient.setStart(0, 0)
        self._gradient.setFinalStop(0, r.height())
        painter.setBrush(self._gradient)
        painter.drawRoundedRect(sliderRect.adjusted(2.5 * margin, 2.5 * margin, -2.5 * margin, - 2.5 * margin), 5, 15)

        # draw text
        if self.animation.state() == QPropertyAnimation.Running:
            return #don't draw any text while animation is running

        font = self._qPointer.font()
        self._gradient.setColorAt(0, light)
        self._gradient.setColorAt(1, shadow)
        self._gradient.setStart(0, r.height() / 2.0 + font.pointSizeF())
        self._gradient.setFinalStop(0, r.height() / 2.0 - font.pointSizeF())
        painter.setFont(font)
        painter.setPen(QPen(QBrush(self._gradient), 0))

        if self._qPointer.isChecked():
            painter.drawText(0, 0, r.width() / 2, r.height()-1, Qt.AlignCenter, "ON")
        else:
            painter.drawText( r.width() / 2, 0, r.width() / 2, r.height() - 1, Qt.AlignCenter, "OFF")

    def updateSliderRect(self, size):
        self._sliderShape.setWidth(size.width() / 2.0)
        self._sliderShape.setHeight(size.height() - 1.0)

    @pyqtSlot(bool, name='animate')
    def animate(self, checked):
        self.animation.setDirection = QPropertyAnimation.Forward if checked else QPropertyAnimation.Backward
        print(self.animation.setDirection)
        self.animation.start()


class QSlideSwitch(QAbstractButton):
    def __init__(self, parent = None):
        super(QAbstractButton, self).__init__(parent)

        self.d_ptr = QSlideSwitchPrivate( self )
        self.clicked.connect( self.d_ptr.animate )
        self.d_ptr.animation.finished.connect( self.update )

    def __del__(self):
        del self.d_ptr

    def sizeHint(self):
        return QSize(48, 28)

    def hitButton(self, point):
        return self.rect().contains(point)

    def paintEvent(self, event):
        painter = QPainter(self)
        painter.setRenderHint(QPainter.Antialiasing)
        self.d_ptr.drawSlider(painter)

    def resizeEvent(self, event):
        self.d_ptr.updateSliderRect(event.size())
        self.repaint()


if __name__ == '__main__':

    import sys

    app = QApplication(sys.argv)

    switcher = QSlideSwitch()
    switcher.setCheckable(True)
    switcher.show()

    sys.exit(app.exec_())