code: def device(self):
      if self._device is None:
          if self.use_cuda:
              device = backend.GpuDevice.from_device_id(
                  self.cuda_device
              )
          elif self.use_chainerx:
              device = backend.ChainerxDevice(
                  chainerx.get_device(self.chainerx_device)
              )
          elif self.use_ideep != "never":
              device = backend.Intel64Device()
          else:
              device = backend.CpuDevice()
          self._device = device
      return self._device
  
imports: import functools
  import chainer
  from chainer import backend
  from chainer.testing import _bundle
  from chainer.testing import attr
  import chainerx
label_desc: Use image node_id 5 for calling the BackendConfig obj's underlying member method code with example usage: obj.device() and returns: self