code: def get_src_builders(self, env):
          
          memo_key = id(env)
          try:
              memo_dict = self._memo['get_src_builders']
          except KeyError:
              memo_dict = {}
              self._memo['get_src_builders'] = memo_dict
          else:
              try:
                  return memo_dict[memo_key]
              except KeyError:
                  pass
  
          builders = []
          for bld in self.src_builder:
              if SCons.Util.is_String(bld):
                  try:
                      bld = env['BUILDERS'][bld]
                  except KeyError:
                      continue
              builders.append(bld)
  
          memo_dict[memo_key] = builders
          return builders
docs: Returns the list of source Builders for this Builder.
  
          This exists mainly to look up Builders referenced as
          strings in the 'BUILDER' variable of the construction
          environment and cache the result.