code: def _assert_backend(backend: str) -> None:
      backends = available_backends()
      if backend not in backends:
          raise ValueError(f"Backend should be one of '{backends}'")
  
imports: import socket
  from contextlib import contextmanager
  from functools import wraps
  from typing import Any, Callable, List, Mapping, Optional, Tuple, Union
  import torch
  from ignite.distributed.comp_models import _SerialModel, has_hvd_support, has_native_dist_support, has_xla_support, registered_computation_models
  from ignite.utils import setup_logger
label_desc: Use image node_id 21 for calling a global function with example usage: _assert_backend(backend) without return types