code: def translate_reaction(reaction, metabolite_mapping):
      
      # Transport reactions where the same metabolite occurs in different
      # compartments should have been filtered out but just to be sure, we add
      # coefficients in the mapping.
      stoichiometry = defaultdict(float)
      for met, coef in iteritems(reaction.metabolites):
          kegg_id = metabolite_mapping.setdefault(met, map_metabolite2kegg(met))
          if kegg_id is None:
              continue
          stoichiometry[kegg_id] += coef
      return dict(stoichiometry)
docs: Return a mapping from KEGG compound identifiers to coefficients.
  
      Parameters
      ----------
      reaction : cobra.Reaction
          The reaction whose metabolites are to be translated.
      metabolite_mapping : dict
          An existing mapping from cobra.Metabolite to KEGG compound identifier
          that may already contain the metabolites in question or will have to be
          extended.
  
      Returns
      -------
      dict
          The stoichiometry of the reaction given as a mapping from metabolite
          KEGG identifier to coefficient.