code: def obj_box_coord_rescale(coord=None, shape=None):
      
      if coord is None:
          coord = []
      if shape is None:
          shape = [100, 200]
  
      return obj_box_coords_rescale(coords=[coord], shape=shape)[0]
docs: Scale down one coordinates from pixel unit to the ratio of image size i.e. in the range of [0, 1].
      It is the reverse process of ``obj_box_coord_scale_to_pixelunit``.
  
      Parameters
      ------------
      coords : list of 4 int or None
          One coordinates of one image e.g. [x, y, w, h].
      shape : list of 2 int or None
          For [height, width].
  
      Returns
      -------
      list of 4 numbers
          New bounding box.
  
      Examples
      ---------
      >>> coord = tl.prepro.obj_box_coord_rescale(coord=[30, 40, 50, 50], shape=[100, 100])
        [0.3, 0.4, 0.5, 0.5]