python mysqldb cursor messages list shows errors twice

Question

For some reason whenever i run a query on the db cursor, it generates two errors in its .messages list, is this a feature?

here is the code that runs the query, all the application does is open a connection to the db, run this once with a forced error, read the .messages, then exit

import MySQLdb

class dbobject:
    def __init__(self, dbhost, dbuser, dbpass, dbname):
        self.connection = MySQLdb.connect( user=dbuser, passwd=dbpass, host=dbhost, db=dbname )
        self.cursor = self.connection.cursor()

    def try_query(self, query, args=()):
        """ attempts to run a query, where
                query is the query to be run, with '%s' statements where the values should be, and
                args is a tuple of the values to go with the query"""
        try:
            if args == ():
                self.cursor.execute(query)
            else:
                self.cursor.execute(query, args)
            self.connection.commit()
        except:

            self.connection.rollback()

    def add_unit(self, name, version, credits):
        """ takes name, version, credits
                name is the name of the unit paper
                version is the unit version, and
                credits is how many credits its worth"""
        self.try_query("insert into dsfdf tbl_unit (unit_name, unit_version, unit_credits) values (%s,%s,%s)",(name,version,credits))

    def close(self):
        self.cursor.close()
        self.connection.close()


blah = dbobject(#####################)
blah.add_unit( "thing", "something", 6)
for i in blah.cursor.messages:
    print i
blah.close()

Answer 1

Perhaps you can post the message(s) you receive.

mysql_insert_etc.py:22: Warning: Data truncated for column 'val' at row 1
self.cursor.execute(query, args) (, ('Warning', 1265L, "Data truncated for column 'val' at row 1"))

From the above (manufactured error) it appears that MySQLdb returns:

1. the MySQL warning, and
2. its own exception.

Using the code below you can either suppress warnings, or have them raise exceptions.

Raise an exception (slightly modified from this example):

from warnings import catch_warnings, simplefilter

def try_query(self, query, args=()):
    with catch_warnings():
        simplefilter('error', MySQLdb.Warning)
        try:
            if args == ():
                self.cursor.execute(query)
            else:
                self.cursor.execute(query, args)
            self.connection.commit()
        except MySQLdb.Error, e:
            self.connection.rollback()
            raise e

Suppress warnings (from here):

from warnings import filterwarnings

filterwarnings('ignore', category=MySQLdb.Warning)