code: def find_metabolites_not_consumed_with_open_bounds(model):
      
      mets_not_consumed = list()
      helpers.open_exchanges(model)
      for met in model.metabolites:
          with model:
              exch = model.add_boundary(
                  met, type="irrex", reaction_id="IRREX", lb=-1000, ub=0)
              solution = helpers.run_fba(model, exch.id, direction="min")
              if np.isnan(solution) or abs(solution) < TOLERANCE_THRESHOLD:
                  mets_not_consumed.append(met)
      return mets_not_consumed
docs: Return metabolites that cannot be consumed with open boundary reactions.
  
      When all metabolites can be secreted, it should be possible for each and
      every metabolite to be consumed in some form.
  
      Parameters
      ----------
      model : cobra.Model
          The metabolic model under investigation.
  
      Returns
      -------
      list
          Those metabolites that could not be consumed.