code: def metric_func(self):
      self._metric_func = {"loss": min}
      return self._metric_func
  
imports: import os
  import torchnet
  import torch
  from typing import Dict, Any
  import wandb
  from torch.utils.tensorboard import SummaryWriter
  import logging
  from torch_points3d.models import model_interface
label_desc: Use image node_id 4 for calling the BaseTracker obj's underlying member method code with example usage: obj.metric_func() and returns: self