How to pickle QPixmap object dict in Python 3

Question

I want to pickle QPixmap object dict in Python 3

For example,

ImageQpixmapDict = {}
ImageQpixmapDict['XXX'] = QPixmap() 

In this situation, I want to pickle ImageQpixmapDict variable

like

pickle.dump(ImageQpixmapDict, 'filePath')

I tried to pickle QPixmap object by using QSettings, but it doesn't work.

But as you know, QPixmap object couldn't be pickled. So, How can I solve this problem.

Answer 1

Only some Qt classes are pickable (see the docs) and among them there is no QPixmap so a solution is to create a derived class that implements that logic:

import pickle
from PyQt5 import QtCore, QtGui


class Pickable_QPixmap(QtGui.QPixmap):
    def __reduce__(self):
        return type(self), (), self.__getstate__()

    def __getstate__(self):
        ba = QtCore.QByteArray()
        stream = QtCore.QDataStream(ba, QtCore.QIODevice.WriteOnly)
        stream << self
        return ba

    def __setstate__(self, ba):
        stream = QtCore.QDataStream(ba, QtCore.QIODevice.ReadOnly)
        stream >> self


if __name__ == "__main__":
    import sys

    app = QtGui.QGuiApplication(sys.argv)

    # create QPixmap
    pixmap = QtGui.QPixmap(100, 100)
    pixmap.fill(QtGui.QColor("red"))

    with open("data.pickle", "wb") as f:

        image_dict = dict()
        image_dict["XXX"] = Pickable_QPixmap(
            pixmap
        )  # convert QPixmap to Pickable_QPixmap
        pickle.dump(image_dict, f)

    with open("data.pickle", "rb") as f:
        image_dict = pickle.load(f)
        pixmap = image_dict["XXX"]

        qpixmap = QtGui.QPixmap(pixmap)  # convert Pickable_QPixmap to QPixmap

        assert qpixmap.size() == pixmap.size() == QtCore.QSize(100, 100)
        assert qpixmap.toImage() == pixmap.toImage()