HI There, Maybe I should not post this in the dev group, but I think it has some relationship on the Python core. I'm using MySQLdb as the MySQL client. Recently I got a weird problem of this library. After looking into it, I suspect the problem may related to the conversion from unsigned long to PyLongObject. Here is the detail, If you are familiar with MySQLdb, the following snippet is a way to query the data from MySQL: connection = MySQLdb.connect(...) connection.autocommit(True) try: cursor = connection.cursor() if not cursor.execute(sql, values) > 0: return None row = cursor.fetchone() finally: connection.close() return row[0] Sometimes the return value of execute method would be 18446744073709552000 even there is no matched data available. I checked the source code of the library, the underlying implementation is https://github.com/farcepest/MySQLdb1/blob/master/_mysql.c#L835, static PyObject * _mysql_ConnectionObject_affected_rows( _mysql_ConnectionObject *self, PyObject *args) { if (!PyArg_ParseTuple(args, "")) return NULL; check_connection(self); return PyLong_FromUnsignedLongLong(mysql_affected_rows(&(self-> connection))); } And here is the official doc for mysql_affected_rows http://dev.mysql.com/doc/refman/5.7/en/mysql-affected-rows.html. Let me give a superficial understanding, please correct me if I were wrong. In a 64-bit system, the mysql_affected_rows is supposed to return a number of unsigned long, which means the range should be 0 ~ 2^64 (18446744073709551616), How could it be possible the function PyLong_FromUnsignedLongLong return a converted value larger than 2^64, that's what I don't understand. Does anyone have some ideas of it? The versions of the components I used: Python: 2.7.6 MySQL 5.7.11 MySQLdb 1.2.5 Thanks