code: def get_current_validator():
      """
      Return the default validator based on the value of an environment variable.
      """
      validator_name = os.environ.get(
          "NBFORMAT_VALIDATOR", "fastjsonschema"
      )
      return _validator_for_name(validator_name)
  
file_path: nbformat/nbformat/json_compat.py
imports: from __future__ import annotations
  import os
  import fastjsonschema
  import jsonschema
  from fastjsonschema import JsonSchemaException
  from jsonschema import Draft4Validator
  from jsonschema.exceptions import ErrorTree, ValidationError
label_desc: Use image node_id 2 for calling a global function with example usage: get_current_validator() and returns: _validator_for_name