trapping a MySql warning

Question

Hi all

In my python script I would like to trap a "Data truncated for column 'xxx'" warning durnig my query using MySql.

I saw some posts suggesting the code below, but it doesn' work.

Do you know if some specific module must be imported or if some option/flag should be called before using this code?

Thanks all

Afeg

import MySQLdb
try:
    cursor.execute(some_statement)
    # code steps always here: No Warning is trapped
    # by the code below
except MySQLdb.Warning, e:
    # handle warnings, if the cursor you're using raises them
except Warning, e:
    # handle warnings, if the cursor you're using raises them

Answer 1

Warnings are just that: warnings. They get reported to (usually) stderr, but nothing else is done. You can't catch them like exceptions because they aren't being raised.

You can, however, configure what to do with warnings, and turn them off or turn them into exceptions, using the warnings module. For instance, warnings.filterwarnings('error', category=MySQLdb.Warning) to turn MySQLdb.Warning warnings into exceptions (in which case they would be caught using your try/except) or 'ignore' to not show them at all. You can (and probably should) have more fine-grained filters than just the category.

Answer 2

Have you tried using MySQL's SHOW WARNINGS command?

Answer 3

I would try first to set the sql_mode. You can do this at the session level. If you execute a:

SET @@sql_mode:=TRADITIONAL;

(you could also set it at the server level, but you need access to the server to do that. and, that setting an still be overridden at the session level, so the bottom line is, always set it at the session level, immediately after establishing the connection)

then many things that are normally warnings become errors. I don't know how those manifest themselves at the python level, but the clear advantage is that the changes are not stored in the database. See: http://dev.mysql.com/doc/refman/5.1/en/server-sql-mode.html#sqlmode_traditional

Answer 4

Stop using MySQLdb. It has such stupid behavior as truncating data and issuing only a warning. Use oursql instead.