def FilterStations(MasterStationList,data_files):
    """
    Filter the files to download by those stations required

    If station of remote file exists in master list, want to download, 
    else not.    
    """

    DownloadStationList=[]
    for dfile in data_files:
        station=dfile.filen.split('.')[0][:-5]
        if station in MasterStationList:
            # We want this file
            DownloadStationList.append(dfile)

    return DownloadStationList