[Python-Dev] Convert from unsigned long long to PyLong

[Tian JiaLin]

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
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