def _is_lt(series, value):
    """ Returns the index of rows from series where series < value.

    Parameters
    ----------
    series : pandas.Series
        The data to be queried

    value : list-like
        The values to be tested

    Returns
    -------
    index : pandas.index
        The index of series for rows where series < value.
    """
    series = series[series.lt(value)]
    return series.index