Can't listdir a file

Raise code

        return self.exists() and not self.is_dir()

    def exists(self):
        return self.at in self.root._name_set()

    def iterdir(self):
        if not self.is_dir():
            raise ValueError("Can't listdir a file")
        subs = map(self._next, self.root.namelist())
        return filter(self._is_child, subs)

    def __str__(self):
        return posixpath.join(self.root.filename, self.at)

    def __repr__(self):