code: def new_label_descriptors(defaults, keys):
      
      label_descriptors = []
      for lk in itertools.chain.from_iterable((defaults.keys(), keys)):
          label = {}
          label["key"] = sanitize_label(lk.key)
          label["description"] = lk.description
          label_descriptors.append(label)
  
      return label_descriptors
docs: create labels for the metric_descriptor
          that will be sent to Stackdriver Monitoring