docs: def ToDeltas(self):
      """Convert the sequence to the sequence of differences between points.
  
      The value of each point v[i] is replaced by v[i+1] - v[i], except for the
      last point which is dropped.
      """
      if len(self.data) < 2:
        self.data = []
        return
      for i in range(0, len(self.data) - 1):
        if self.data[i][0] is None or self.data[i + 1][0] is None:
          self.data[i][0] = None
        else:
          self.data[i][0] = self.data[i + 1][0] - self.data[i][0]
      del self.data[-1]