code: def roundness2(self):
          
  
          if np.isnan(self.hx) or np.isnan(self.hy):
              return np.nan
          else:
              return 2.0 * (self.hx - self.hy) / (self.hx + self.hy)
docs: The star roundness.
  
          This roundness parameter represents the ratio of the difference
          in the height of the best fitting Gaussian function in x minus
          the best fitting Gaussian function in y, divided by the average
          of the best fitting Gaussian functions in x and y.  A circular
          source will have a zero roundness.  A source extended in x or y
          will have a negative or positive roundness, respectively.