code: def sumSeries(requestContext, *seriesLists):
      
      if not seriesLists or not any(seriesLists):
          return []
      seriesList, start, end, step = normalize(seriesLists)
      name = "sumSeries(%s)" % formatPathExpressions(seriesList)
      values = (safeSum(row) for row in zip_longest(*seriesList))
      series = TimeSeries(name, start, end, step, values)
      series.pathExpression = name
      return [series]
docs: Short form: sum()
  
      This will add metrics together and return the sum at each datapoint. (See
      integral for a sum over time)
  
      Example::
  
          &target=sum(company.server.application*.requestsHandled)
  
      This would show the sum of all requests handled per minute (provided
      requestsHandled are collected once a minute).     If metrics with different
      retention rates are combined, the coarsest metric is graphed, and the sum
      of the other metrics is averaged for the metrics with finer retention
      rates.