docs: def size(self, size=None):
          """Returns or sets (if a value is provided) the diameter of the series'
          data points.
  
          :param Number size: If given, the series' size will be set to\
          this.
          :rtype: ``Number``"""
  
          if size is None:
              return self._size
          else:
              if not is_numeric(size):
                  raise TypeError(
                   "size must be number, not '%s'" % str(size)
                  )
              self._size = size