code: def devices(
      backend: str | xla_client.Client | None = None,
  ) -> list[xla_client.Device]:
      """Returns a list of all devices for a given backend.
  
      .. currentmodule:: jaxlib.xla_extension
  
      Each device is represented by a subclass of :class:`Device` (e.g.
      :class:`CpuDevice`, :class:`GpuDevice`). The length of the returned list is
      equal to ``device_count(backend)``. Local devices can be identified by
      comparing :attr:`Device.process_index` to the value returned by
      :py:func:`jax.process_index`.
  
      If ``backend`` is ``None``, returns all the devices from the default backend.
      The default backend is generally ``'gpu'`` or ``'tpu'`` if available,
      otherwise ``'cpu'``.
  
      Args:
        backend: This is an experimental feature and the API is likely to change.
          Optional, a string representing the xla backend: ``'cpu'``, ``'gpu'``, or
          ``'tpu'``.
  
      Returns:
        List of Device subclasses.
      """
      return get_backend(backend).devices()
  
imports: from __future__ import annotations
  from __future__ import annotations
  from collections.abc import Mapping
  import dataclasses
  from functools import lru_cache, partial
  import importlib
  import json
  import logging
  import os
  import pkgutil
  import platform
  import sys
  import threading
  from typing import Any, Callable, Union
  import warnings
  from jax._src import config
  from jax._src import distributed
  from jax._src import traceback_util
  from jax._src import util
  from jax._src import hardware_utils
  from jax._src.cloud_tpu_init import maybe_import_libtpu
  from jax._src.lib import cuda_versions
  from jax._src.lib import xla_client
  from jax._src.lib import xla_extension
  from jax._src.lib import xla_extension_version
label_desc: Use image node_id 27 for calling a global function with example usage: devices(backend) and returns: get_backend