code: def constantLine(requestContext, value):
      
      name = "constantLine(%s)" % str(value)
      start = int(epoch(requestContext['startTime']))
      end = int(epoch(requestContext['endTime']))
      step = int((end - start) / 2.0)
      series = TimeSeries(str(value), start, end, step, [value, value, value])
      series.pathExpression = name
      return [series]
docs: Takes a float F.
  
      Draws a horizontal line at value F across the graph.
  
      Example::
  
          &target=constantLine(123.456)