code: def preview(self):
          
          win_name = 'Camera'
          cv2.namedWindow(win_name, cv2.WINDOW_AUTOSIZE)
          cv2.moveWindow(win_name,20,20)
          self.open()
          while(self.isOpened()):
              cv2.imshow(win_name,self._stream.read()[1])
              if cv2.waitKey(25) & 0xFF == ord('q'):
                  break
          cv2.waitKey()
          cv2.destroyAllWindows()
          cv2.waitKey()
docs: Blocking function. Opens OpenCV window to display stream.