def register_id(self, id_string):
        """Register a manually assigned id as used, to avoid collisions.
        """
        try:
            prefix, count = id_string.rsplit("_", 1)
            count = int(count)
        except ValueError:
            # We don't need to worry about ids that don't match our pattern
            pass
        else:
            if prefix == self.prefix:
                self.counter = max(count, self.counter)
Register a manually assigned id as used, to avoid collisions.