code: def get_coefficient(self, metabolite_id):
          
          if isinstance(metabolite_id, Metabolite):
              return self._metabolites[metabolite_id]
  
          _id_to_metabolites = {m.id: m for m in self._metabolites}
          return self._metabolites[_id_to_metabolites[metabolite_id]]
docs: Return the stoichiometric coefficient of a metabolite.
  
          Parameters
          ----------
          metabolite_id : str or cobra.Metabolite