def _tab(max_i=None):
    """Extraction and caching of IAU1980 nutation coefficients
    """

    filepath = Path(__file__).parent / "data" / "tab5.1.txt"

    result = []
    with filepath.open() as fhd:
        i = 0
        for line in fhd.read().splitlines():
            if line.startswith("#") or not line.strip():
                continue

            fields = line.split()
            result.append(([int(x) for x in fields[:5]], [float(x) for x in fields[6:]]))

            i += 1
            if max_i and i >= max_i:
                break

    return result
Extraction and caching of IAU1980 nutation coefficients