code: def on_train_epoch_start(self) -> None:
      # Set model to eval mode to disable norm layer updates.
      self.model.eval()
  
      # Reset features and targets.
      self._train_features = []
      self._train_targets = []
      self._train_features_tensor = None
      self._train_targets_tensor = None
  
file_path: lightly/lightly/utils/benchmarking/knn_classifier.py
imports: from typing import Tuple, Union
  import torch
  import torch.nn.functional
  from pytorch_lightning import LightningModule
  from torch import Tensor
  from torch.nn import Module
  from lightly.utils.benchmarking import knn_predict
  from lightly.utils.benchmarking.topk import mean_topk_accuracy
label_desc: Use image node_id 5 for calling the KNNClassifier obj's underlying member method code with example usage: obj.on_train_epoch_start() without return types