code: def add_data_point(self, x, y, size, number_format=None):
          
          data_point = BubbleDataPoint(self, x, y, size, number_format)
          self.append(data_point)
          return data_point
docs: Append a new BubbleDataPoint object having the values *x*, *y*, and
          *size*. The optional *number_format* is used to format the Y value.
          If not provided, the number format is inherited from the series data.