def reducer(self, key, values):
        yield key, sum(values)
Raises an error
dataset/ETHPy150Open spotify/luigi/examples/top_artists.py/AggregateArtistsHadoop.reducer--crossover with--dataset/ETHPy150Open cloudera/hue/desktop/core/ext-py/tablib-0.10.0/tablib/packages/odf/element.py/Childless.insertBefore