def _removecleaner(self, cleaner):
        """
        Remove the cleaner from the list if it already exists. Returns True if
        the cleaner was removed.
        """
        oldlen = len(self._old_cleaners)
        self._old_cleaners = [
            oldc for oldc in self._old_cleaners
            if not oldc.issame(cleaner)
        ]
        return len(self._old_cleaners) != oldlen
Remove the cleaner from the list if it already exists. Returns True if
        the cleaner was removed.