def _load_id_map(id_map_path):
    """id_map_path is the path to a file with ``key id'' format
    output is a dictionary map from id (int) to key (str)"""
    id_map = {}
    with open(id_map_path) as f:
        id_content = f.readlines()
    for l in id_content:
        l = l.split(' ')
        id_map[int(l[1])] = l[0]
    return id_map