code: def description(self):
          
  
          if 'metrics' in self.raw:
              metrics = self.raw['metrics']
              head = metrics[0:-1] or metrics[0:1]
              text = ", ".join(head)
              if len(metrics) > 1:
                  tail = metrics[-1]
                  text = text + " and " + tail
          else:
              text = 'n/a'
  
          return text
docs: A list of the metrics this query will ask for.