code: def _find_impl(cls, registry):
      
      mro = _compose_mro(cls, registry.keys())
      match = None
      for t in mro:
          if match is not None:
              # If *match* is an implicit ABC but there is another unrelated,
              # equally matching implicit ABC, refuse the temptation to guess.
              if (  # :off
                  t in registry and
                  t not in cls.__mro__ and
                  match not in cls.__mro__ and
                  not issubclass(match, t)
              ):  # :on
                  raise RuntimeError("Ambiguous dispatch: {0} or {1}".format(match, t))
              break
          if t in registry:
              match = t
      return registry.get(match)
docs: Returns the best matching implementation from *registry* for type *cls*.
  
      Where there is no registered implementation for a specific type, its method
      resolution order is used to find a more generic implementation.
  
      Note: if *registry* does not contain an implementation for the base
      *object* type, this function may return None.