code: def reducer_output(self, metro, values):
          
          records = []
          # build up list of data for each metro area and submit as one network
          # call instead of individually 
          for value in values:
              total, poi = value
              records.append(dict(
                  metro_area=metro,
                  poi=poi,
                  count=total
              ))
              output = "{0}\t{1}\t{2}"
              output = output.format(metro.encode('utf-8'), total, poi.encode('utf-8'))
              yield None, output
          if self.mongo:
              self.mongo.insert_many(records)
docs: store each record in MongoDB and output tab delimited lines