code: def _add_serve_context_tag_values(
      tag_keys: Tuple, tags: Dict[str, str]
  ):
      """Add serve context tag values to the metric tags"""
  
      _request_context = ray.serve.context._serve_request_context.get()
      if ROUTE_TAG in tag_keys and ROUTE_TAG not in tags:
          tags[ROUTE_TAG] = _request_context.route
  
imports: from typing import Dict, List, Optional, Tuple, Union
  import ray
  from ray.serve import context
  from ray.util import metrics
  from ray.util.annotations import PublicAPI
label_desc: Use image node_id 3 for calling a global function with example usage: _add_serve_context_tag_values(tag_keys, tags) without return types