code: def get_backend(backend: str) -> OCIBuilder:
      """
      Get a given backend.
  
      Raises:
          ``ValueError``: If given backend is not available in backend registry.
      """
      if isinstance(backend, OCIBuilder):
          if backend not in BUILDER_REGISTRY.values():
              logger.warning(
                  "Backend '%s' not registered. To use with 'bentoml.container.build', make sure to regsiter it with 'bentoml.container.register_backend'",
                  backend,
              )
          return backend
      if backend not in BUILDER_REGISTRY:
          raise ValueError(
              f"Backend {backend} not registered. Available backends: {REGISTERED_BACKENDS}."
          )
      return BUILDER_REGISTRY[backend]
  
imports: from __future__ import annotations
  import contextlib
  import importlib
  import logging
  import os
  import sys
  import types
  import typing
  from typing import TYPE_CHECKING
  import fs
  import fs.mirror
  from simple_di import Provide
  from simple_di import inject
  from ...exceptions import InvalidArgument
  from ..configuration.containers import BentoMLContainer
  from ..utils import bentoml_cattr
  from .base import OCIBuilder
  from .generate import generate_containerfile
label_desc: Use image node_id 12 for calling a global function with example usage: get_backend(backend) and returns: BUILDER_REGISTRY, backend