Return the filename of the cache for bucket contents.
    Create the path if it does not exist.

def _get_buckets_cache_filename():
    '''
    Return the filename of the cache for bucket contents.
    Create the path if it does not exist.
    '''

    cache_dir = _get_cache_dir()
    if not os.path.exists(cache_dir):
        os.makedirs(cache_dir)

    return os.path.join(cache_dir, 'buckets_files.cache')