In QwtStyleSheetRecorder.drawRects() Replace self.border.rectList += rects[i] with self.border.rectList.append(rects[i]) or with self.border.rectList += [rects[i]]
In QwtStyleSheetRecorder.drawRects()
Replace
self.border.rectList += rects[i]
with
self.border.rectList.append(rects[i])
or with
self.border.rectList += [rects[i]]