Resize an image to a square image with the help of minimal padding

resize.py

from PIL import Image

def resize_image(img_path, desired_size = 300, background_color=None):
  img = Image.open(img_path)

  old_size = img.size

  if background_color == None:
    background_color = img.load()[0,0]

  ratio = float(desired_size-10)/max(old_size)
  new_size = tuple([int(x*ratio) for x in old_size])
  img = img.resize(new_size, Image.ANTIALIAS)

  output = Image.new("RGB", (desired_size, desired_size), color=background_color)
  output.paste(img, ((desired_size-new_size[0])//2, (desired_size-new_size[1])//2))

  return output

if __name__ == '__main__':
    img = resize_image("image.png", background_color=(255, 255, 255))
    img.show()