code: def spark_backend(op):
      from hail.backend.spark_backend import SparkBackend
  
      b = Env.backend()
      if isinstance(b, SparkBackend):
          return b
      else:
          raise NotImplementedError(
              f"{b.__class__.__name__} doesn't support {op}, only SparkBackend"
          )
  
imports: from typing import Optional, Union
  import sys
  import re
  from hailtop.config import ConfigVariable, configuration_of
label_desc: Use image node_id 7 for calling the Env obj's underlying member method code with example usage: obj.spark_backend(op) and returns: b