docs: def load_network_model(model):
      '''
      Loads metabolic network models in metabolitics.
  
      :param str model: model name
      '''
      if type(model) == str:
          if model in ['ecoli', 'textbook', 'salmonella']:
              return cb.test.create_test_model(model)
          elif model == 'recon2':
              return cb.io.load_json_model('%s/network_models/%s.json' %
                                           (DATASET_PATH, model))
      if type(model) == cb.Model:
          return model