If the user passes a freq and another freq is inferred from passed data,
    require that they match.

    Parameters
    ----------
    freq : DateOffset or None
    inferred_freq : DateOffset or None
    freq_infer : bool

    Returns
    -------
    freq : DateOffset or None
    freq_infer : bool

    Notes
    -----
    We assume at this point that `maybe_infer_freq` has been called, so
    `freq` is either a DateOffset object or None.

def validate_inferred_freq(freq, inferred_freq, freq_infer):
    """
    If the user passes a freq and another freq is inferred from passed data,
    require that they match.

    Parameters
    ----------
    freq : DateOffset or None
    inferred_freq : DateOffset or None
    freq_infer : bool

    Returns
    -------
    freq : DateOffset or None
    freq_infer : bool

    Notes
    -----
    We assume at this point that `maybe_infer_freq` has been called, so
    `freq` is either a DateOffset object or None.
    """
    if inferred_freq is not None:
        if freq is not None and freq != inferred_freq:
            raise ValueError('Inferred frequency {inferred} from passed '
                             'values does not conform to passed frequency '
                             '{passed}'
                             .format(inferred=inferred_freq,
                                     passed=freq.freqstr))
        elif freq is None:
            freq = inferred_freq
        freq_infer = False

    return freq, freq_infer