def save(self, filename=None):
        filename = Path(filename) if filename is not None else self.filename
        with filename.open("w") as f:
            f.write(self.yaml)
def EVT_MOUSEWHEEL(event):
  global zoomdist
  dy = event.WheelRotation
  zoomdist *= np.power(0.95, -dy)
  refresh()