code: def find_biomass_precursors(model, reaction):
      
      id_of_main_compartment = helpers.find_compartment_id_in_model(model, 'c')
      gam_reactants = set()
      try:
          gam_reactants.update([
              helpers.find_met_in_model(
                  model, "MNXM3", id_of_main_compartment)[0]])
      except RuntimeError:
          pass
      try:
          gam_reactants.update([
              helpers.find_met_in_model(
                  model, "MNXM2", id_of_main_compartment)[0]])
      except RuntimeError:
          pass
  
      biomass_precursors = set(reaction.reactants) - gam_reactants
  
      return list(biomass_precursors)
docs: Return a list of all biomass precursors excluding ATP and H2O.
  
      Parameters
      ----------
      reaction : cobra.core.reaction.Reaction
          The biomass reaction of the model under investigation.
      model : cobra.Model
          The metabolic model under investigation.
  
      Returns
      -------
      list
          Metabolite objects that are reactants of the biomass reaction excluding
          ATP and H2O.