def inspect_last(self, stream, only_allocated=False):
        if only_allocated:
            found = False
            for walker in self._virtual_walkers:
                if walker.matches(stream):
                    found = True
                    break
            if not found:
                raise UnresolvedIdentifierError("inspect_last could not find an allocated virtual streamer for the desired stream", stream=stream)
        if stream in self._last_values:
            return self._last_values[stream]
        raise StreamEmptyError(u"inspect_last called on stream that has never been written to", stream=stream)