def METHOD_NAME(chunk_idx, t1_file, chunksize, h5key):
    # print("Processing chunk #{}".format(chunk_idx))
    with pd.HDFStore(t1_file, 'r') as store:
        start = chunk_idx * chunksize
        stop = (chunk_idx + 1) * chunksize
        # print("start: {}  stop: {}".format(start, stop))
        chunk = pd.read_hdf(t1_file, h5key,
                            where='index >= {} & index < {}'.format(start, stop))
    pyg = pygama.VectorProcess(default_list=True)
    t1_df = pyg.Process(chunk)
    return t1_df