python——如何将列表作为新列附加到Excel中？

StructuredSecuritiesWaterfallReserveAccountStructuredSecuritiesWaterfall.

for tranche, reserve in zip(StructuredSecuritiesWaterfall, ReserveAccount):
    # since it is list of list, we need to flatten it first
    flattened_tranche = [item for sublist in tranche for item in sublist]
    fp.write(','.join(map(str, list(itertools.chain(flattened_tranche))) + 
                      [str(reserve)]) + '\n')

我试过上面的方法，但是unsupported operand type(s) for +: 'map' and 'list'.关于如何达到目的有什么想法吗？