def _get_new_index(busy_indices, start_index=0, limit=100):
    """Returns lowest integer lower than limit not in busy_indices list.

    Parameters
    ----------
    busy_indices : list of int
    limit : int (default 100)

    Returns
    -------
    int

    Examples
    --------

        >>> _get_new_index([0, 1, 2, 3], limit=100)
        4
        >>> _get_new_index([0, 2, 3, 4], limit=100)
        1

    """
    i = start_index
    while i < limit:
        if i not in busy_indices:
            break
        i += 1
    return i