def create_filename(ticker, interval, mmyy):
    """
    Create a filename based on a set of given parameter values.
    :param ticker: the ticker symbol
    :param interval: the time interval of the data
    :param mmyy: the date (in mmyy format) for which data is being fetched
    :return: filename string
    """
    return f"{ticker}_{interval}_{mmyy[2:]}{mmyy[0:2]}.DAT"