code: def calculate_identifier(obj: Any) -> str:
      """Calculate a url-safe identifier for an object."""
  
      # Task 1: Serialize the object.
      # Task 2: Calculate its sha256 hash.
      # Task 3: Get the url safe, base64 representation of it.
  
      # TODO (Alex): Ideally we should use the existing ObjectRef serializer to
      # avoid duplicate serialization passes and support nested object refs.
      m = hashlib.sha256()
      m.update(cloudpickle.dumps(obj))
      hash = m.digest()
      encoded = base64.urlsafe_b64encode(hash).decode("ascii")
      return encoded
  
imports: import base64
  import json
  from ray import cloudpickle
  from enum import Enum, unique
  import hashlib
  from typing import Dict, Optional, Any, Tuple
  from dataclasses import dataclass
  import ray
  from ray import ObjectRef
  from ray._private.utils import get_or_create_event_loop
  from ray.util.annotations import PublicAPI
label_desc: Use image node_id 4 for calling a global function with example usage: calculate_identifier(obj) and returns: encoded