code: def _get_backend():
      if os.environ.get(FASTNLP_BACKEND, None) != None:
          backend = os.environ.get(FASTNLP_BACKEND)
          logger.debug(
              f"Get Dataloader backend:{backend} from os.environ"
          )
      else:
          available_backends = set()
          for module in sys.modules.values():
              _backend = _check_module(module)
              if _backend:
                  available_backends.add(_backend)
          if len(available_backends) == 1:
              backend = available_backends.pop()
              logger.debug(
                  f"Get Dataloader backend:{backend} from sys.modules."
              )
          elif len(available_backends) > 1:
              raise RuntimeError(
                  "Fail to detect dataloader backend automatically, because multiple backends:"
                  f"{available_backends} has been imported."
              )
          else:
              raise RuntimeError(
                  "Fail to detect dataloader backend automatically, please set it manually."
              )
      return backend
  
file_path: fastNLP/fastNLP/core/dataloaders/prepare_dataloader.py
imports: from typing import Union, Callable
  import os
  import sys
  from .torch_dataloader import prepare_torch_dataloader
  from .paddle_dataloader import prepare_paddle_dataloader
  from .jittor_dataloader import prepare_jittor_dataloader
  from .oneflow_dataloader import prepare_oneflow_dataloader
  from ...envs import FASTNLP_BACKEND, SUPPORT_BACKENDS
  from ..log import logger
label_desc: Use image node_id 3 for calling a global function with example usage: _get_backend() and returns: backend