def createIdPair(df1, dest_col, cols, suffixes = ['_f','_nf']):
    """

    Append flight IDs to the input bookings table.

    Parameters: 

       df1 (pandas.DataFrame) : input dataframe to enhance with flight identifiers
       dest_col (string) : base name of the identifier columns
       cols (list(string)) : columns from which to form the identifier
       suffixes (list(string)) : suffixes to add to the base identifier column header

    Return: 
       A dataframe with two additional identifier columns. 

    The original input remains intact. The number of rows in the returned dataframe
    is identical to the number of rows in the input dataframe.

    The base name has the suffixes added to it according to the parameter `suffixes`.

    """

    df = df1.copy()

    if (len(suffixes) != 2):
        print("length of suffixes must be 2")
        return -1

    col = dest_col+suffixes[0]
    df[col] = df[cols[0]+suffixes[0]]
    for i in range(1,len(cols)):
        df[col] += df[cols[i]+suffixes[0]]

    col = dest_col+suffixes[1]
    df[col] = df[cols[0]+suffixes[1]]
    for i in range(1,len(cols)):
        df[col] += df[cols[i]+suffixes[1]]
    return df