code: def test_forward_with_epoch_num_changes_cost_weight(self):
      # Redefining model. We do not want this to change the state of ``self.model``.
      params = Params.from_file(self.param_file)
      model = Model.from_params(
          vocab=self.vocab, params=params["model"]
      )
      # Initial cost weight, before forward is called.
      assert model._checklist_cost_weight == 0.8
      iterator = EpochTrackingBucketIterator(
          sorting_keys=[["sentence", "num_tokens"]]
      )
      cost_weights = []
      for epoch_data in iterator(self.dataset, num_epochs=4):
          model.forward(**epoch_data)
          cost_weights.append(model._checklist_cost_weight)
      # The config file has ``wait_num_epochs`` set to 0, so the model starts decreasing the cost
      # weight at epoch 0 itself.
      assert_almost_equal(cost_weights, [0.72, 0.648, 0.5832, 0.52488])
  
imports: from __future__ import with_statement
  from __future__ import division
  from __future__ import absolute_import
  from numpy.testing import assert_almost_equal
  import torch
  from allennlp.common import Params
  from allennlp.common.testing import ModelTestCase
  from allennlp.data import Vocabulary
  from allennlp.data.iterators import EpochTrackingBucketIterator
  from allennlp.models import Model
  from allennlp.models.archival import load_archive
label_desc: Use image node_id 6 for calling the NlvrCoverageSemanticParserTest obj's underlying member method code with example usage: obj.test_forward_with_epoch_num_changes_cost_weight() without return types