def file_crc32(filename, chunksize=_CHUNKSIZE):
    """
    calculate the CRC32 of the contents of filename
    """

    check = 0
    with open(filename, 'rb') as fd:
        for data in iter(lambda: fd.read(chunksize), ""):
            check = crc32(data, check)
    return check
calculate the CRC32 of the contents of filename