Python Pillow Image Invert

# -*- encoding:utf-8 -*-import osimport sysfrom PIL import Imagefrom PIL import ImageOpsdef img_gray_invert(img_path):  """  invert input image.  """  if not os.path.isfile(img_path):    print "Error for input file path."    return  image = Image.open(img_path)  image = image.convert("L")  inverted_image = ImageOps.invert(image)  return inverted_imageif __name__ == '__main__':  argv = sys.argv  if len(argv) != 3:    print """Example:    python gray_invert.py test/htc.png test/htc_inv.png    """  else:    img_file_path = argv[1]    invert_image = img_gray_invert(img_file_path)    img_file_out = argv[2]    invert_image.save(img_file_out)