def addBarcodesToIdentifier(read, UMI, cell):
    '''extract the identifier from a read and append the UMI and
    cell barcode before the first space'''

    read_id = read.identifier.split(" ")

    if cell == "":
        read_id[0] = read_id[0] + "_" + UMI
    else:
        read_id[0] = read_id[0] + "_" + cell + "_" + UMI

    identifier = " ".join(read_id)

    return identifier
extract the identifier from a read and append the UMI and
    cell barcode before the first space