code: def assert_optimal(model, message='optimization failed'):
      
      status = model.solver.status
      if status != OPTIMAL:
          exception_cls = OPTLANG_TO_EXCEPTIONS_DICT.get(
              status, OptimizationError)
          raise exception_cls("{} ({})".format(message, status))
docs: Assert model solver status is optimal.
  
      Do nothing if model solver status is optimal, otherwise throw
      appropriate exception depending on the status.
  
      Parameters
      ----------
      model : cobra.Model
          The model to check the solver status for.
      message : str (optional)
          Message to for the exception if solver status was not optimal.