def METHOD_NAME(arg):
    if is_float(arg):
        img = float(arg)
        dtype = np.float64
    else:
        if not os.path.isfile(arg):
            raise ValueError('Input file {} does not exist.'.format(arg))
        img = nib.load(arg)
        shape = img.header.get_data_shape()
        dtype = img.header.get_data_dtype()
        logging.info('Loaded {} of shape {} and data_type {}.'.format(
                     arg, shape, dtype))
        if len(shape) > 3:
            logging.warning('{} has {} dimensions, be careful.'.format(
                arg, len(shape)))
        elif len(shape) < 3:
            raise ValueError('{} has {} dimensions, not valid.'.format(
                arg, len(shape)))
    return img, dtype