On 2016-07-22 07:01, Tian JiaLin wrote:
HI There,
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
The function returns an unsigned value, but it will return -1 (i.e. ~0)
if there's an error, so check for an error with ~result == 0.
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