def dt_s_tup_to_string(dt_s_tup):
    """

    Parameters
    ----------
    dt_s_tup : tuple
        A tuple of length 2.
        The first entry is a string specifying the deterministic term without
        any information about seasonal terms (for example "nc" or "c").
        The second entry is an int specifying the number of seasons.

    Returns
    -------
    dt_string : str
        Returns dt_s_tup[0], if dt_s_tup[1] is 0 (i.e. no seasons).
        If dt_s_tup[1] is > 0 (i.e. there are seasons) add an "s" to the string
        in dt_s_tup[0] like in the following examples:
        "nc" --> "ncs"
        "c" --> "cs"
        "ct" --> "cst"
    """
    dt_string = dt_s_tup[0]  # string for identifying the file to parse.
    if dt_s_tup[1] > 0:  # if there are seasons in the model
        if dt_string == "nc":
            dt_string = dt_string[:2] + "s"
        if dt_string == "c" or dt_string == "ct":
            dt_string = dt_string[:1] + "s" + dt_string[1:]
    return dt_string