def period_to_freq(period):
    """
    1m, 4h 등의 period를 pandas 기반의 D, H, T로 바꿔준다.
    [pandas time 기호]
    B	Business day
    D	Calendar day
    W	Weekly
    M	Month end
    Q	Quarter end
    A	Year end
    BA	Business year end
    AS	Year start
    H	Hourly frequency
    T, min	Minutely frequency
    S	Secondly frequency
    L, ms	Millisecond frequency
    U, us	Microsecond frequency
    N, ns	Nanosecond frequency

    :param period:
    :return:
    """
    return period.replace('m', 'T').upper()
