code: def is_constrained_reaction(model, rxn):
      
      lower_bound, upper_bound = helpers.find_bounds(model)
      if rxn.reversibility:
          return rxn.lower_bound > lower_bound or rxn.upper_bound < upper_bound
      else:
          return rxn.lower_bound > 0 or rxn.upper_bound < upper_bound
docs: Return whether a reaction has fixed constraints.