def time_delta_rule(t=12, period="A"):
    """Return a Rule for resampling, eg t=12 returns "A-Dec
    
    Parameters
    ----------
    t : int, optional
        The month for year-ending rule in time sereis period, by default 12
    period: str, optional
        Whether Annual or Quarter, optional, by default A
    """
    annual_dict = {
        1: "A-Jan",
        2: "A-Feb",
        3: "A-Mar",
        4: "A-Apr",
        5: "A-May",
        6: "A-Jun",
        7: "A-Jul",
        8: "A-Aug",
        9: "A-Sept",
        10: "A-Oct",
        11: "A-Nov",
        12: "A-Dec",
    }

    if period == "A":
        return annual_dict[t]
    else:
        ### place holder for quarterly etc
        return None