def METHOD_NAME(key: str) -> str | None:
    """Returns a sort key used to group urls in 10K batches.
    >>> get_sort_key("/authors/OL123456A")
    'authors_0012'
    """
    if m := re_key.match(key):
        return f"{m.group(1)}_{int(web.numify(key)) // 10000:04}"
    return None