code: def close_boundaries_sensibly(model):
      
      for rxn in model.reactions:
          if rxn.reversibility:
              rxn.bounds = -1, 1
          else:
              rxn.bounds = 0, 1
      for boundary in model.boundary:
          boundary.bounds = (0, 0)
docs: Return a cobra model with all boundaries closed and changed constraints.
  
      In the returned model previously fixed reactions are no longer constrained
      as such. Instead reactions are constrained according to their
      reversibility. This is to prevent the FBA from becoming infeasible when
      trying to solve a model with closed exchanges and one fixed reaction.
  
      Parameters
      ----------
      model : cobra.Model
          The metabolic model under investigation.
  
      Returns
      -------
      cobra.Model
          A cobra model with all boundary reactions closed and the constraints
          of each reaction set according to their reversibility.