QFileDialog's default operation is open file, but "Save to picture" action expects save file instead. Therefore, switch to QtGui.QFileDialog.getSaveFileName()
Moreover, QtGui.QPixmap.grabWindow() is deprecated, use PyQt5.QtWidgets.QApplication.primaryScreen().grabWindow() instead.
Signed-off-by: Amjad Ouled-Ameur aouledameur@baylibre.com