code: def roundness(im):
      
      perimeter = im.shape[0]*2 +im.shape[1]*2 -4
      area = im.size
      return 4*np.pi*area/perimeter**2
docs: from astropy.io import fits as pyfits
      data=pyfits.getdata('j94f05bgq_flt.fits',ext=1)
      star0=data[403:412,423:432]
      star=data[396:432,3522:3558]
      In [53]: findobj.roundness(star0)
      Out[53]: 0.99401955054989544
      In [54]: findobj.roundness(star)
      Out[54]: 0.83091919980660645