from PySide2.QtCore import QByteArray, QIODevice, QDataStream, QCryptographicHash
from PySide2.QtGui import QPixmap
from PySide2.QtWidgets import QApplication

def save(pixmap: QPixmap):
    print("=== save ===")

    print("Saving", pixmap.size())

    data = QByteArray()
    dataStream = QDataStream(data, QIODevice.WriteOnly)
    dataStream << pixmap

    print("Saved size:", data.size())
    print("Saved hash:", QCryptographicHash.hash(data, QCryptographicHash.Md5).toHex())

    return data

def restore(data: QByteArray):
    dataStream = QDataStream(data, QIODevice.ReadOnly)
    pixmap = QPixmap()
    dataStream >> pixmap

    print("=== restored ===")
    print("Image size:", pixmap.size())

    return pixmap

if __name__ == "__main__":
    app = QApplication([])

    pixmapName = "test.png"

    pixmap = QPixmap(pixmapName)
    assert not pixmap.isNull()

    data = save(pixmap)
    pixmap = restore(data)
    assert not pixmap.isNull()

    data = save(pixmap)
    pixmap = restore(data)
    assert not pixmap.isNull()