docs: def _cuda_get_gpu_spec_string(gpu_ids=None):
      """
      Build a GPU id string to be used for CUDA_VISIBLE_DEVICES.
      """
  
      if gpu_ids is None:
          return ''
  
      if isinstance(gpu_ids, list):
          return ','.join(str(gpu_id) for gpu_id in gpu_ids)
  
      if isinstance(gpu_ids, int):
          return str(gpu_ids)
  
      return gpu_ids