code: def fit(self, train_set, validation_set=None, **kwargs):
      raise NotImplementedError()
  
imports: import unittest
  import pytest
  import torch
  import numpy
  from small_text.integrations.pytorch.exceptions import PytorchNotFoundError
label_desc: Use image node_id 3 for calling the PytorchClassifierImplementation obj's underlying member method code with example usage: obj.fit(train_set, validation_set) without return types