Get the block identified by namespace, offset, key and
        value

def get_block(self, namespace, offset, key):
        """Get the block identified by namespace, offset, key and
        value"""
        cursor = self.cursor
        cursor.execute('SELECT data, flags FROM gauged_data '
                       'WHERE namespace = %s AND "offset" = %s AND key = %s',
                       (namespace, offset, key))
        row = cursor.fetchone()
        return (None, None) if row is None else row