[DB-SIG] MySQLdb warnings problem

[Terry Hancock]

Hi all,

I'm in the middle of writing a Zope/MySQL project, and
I use a Python/MySQL crawler to do some database
maintenance tasks.

I'm writing this crawler now, and it's my first
experience with "Python Database API 2.0".

I originally posted this question on the main
python list, not knowing where to ask, but I
was refered here, so I hope someone can give me
a clue as to what's going on with this:

The program is fairly long, but what happens is that
it scans the database for entries in a database table
called "user" and calculates some statistics for them
based on other tables.  All the retrievals work fine,
but I get a funny traceback when I write the data
back into the user's row in the table:

Traceback (most recent call last):
  File "Styx.py", line 258, in ?
    styx.crawl( styx.params['P_Styx'],  styx_tasks)
  File "Crawler.py", line 193, in crawl
    task[1](argval)                     # Operate on it
  File "Styx.py", line 165, in compute_user_stats
    dbcursor.execute(sqlcmd)
  File
"/usr/local/narya/lib/python2.1/site-packages/MySQLdb/cursors.py", line
61, in execute
    r = self._query(query)
  File
"/usr/local/narya/lib/python2.1/site-packages/MySQLdb/cursors.py", line
168, in _query
    rowcount = self._BaseCursor__do_query(q)
  File
"/usr/local/narya/lib/python2.1/site-packages/MySQLdb/cursors.py", line
118, in __do_query
    self._check_for_warnings()
  File
"/usr/local/narya/lib/python2.1/site-packages/MySQLdb/cursors.py", line
150, in _check_for_warnings
    raise Warning, self._info
_mysql_exceptions.Warning: Rows matched: 1  Changed: 0  Warnings: 1

For reference, here's a snippet of the code where this
broke:
	sqlcmd= """
		UPDATE user SET nposts=%d, nrecent=%d, keytopic='%s'
		WHERE username='%s'
		""" % ( n_posts, n_recent, keytopic, user[0] )

	#print sqlcmd
	#try:
	dbcursor.execute(sqlcmd)
	#except:
	#	pass

[It's already been pointed out to me that dbcursor.execute provides
a safer quoting mechanism than I'm using here -- but as the output
below shows, that's definitely not the problem here.]

As the commented-out lines indicate, I tried ignoring this problem.
Doing so seems to make the program work fine, but I can't figure
out why it should be an issue in the first place (and I generally
prefer not to just ignore warnings, especially without understanding
them).

The thing is, what's the warning message?  Nothing was changed
this time, because a previous run already updated the stats (the
first run said "Rows matched: 1  Changed: 1  Warnings: 1").

Uncommenting the print statement shows what the actual SQL was:

  UPDATE user SET nposts=7, nrecent=0, keytopic='/'
  WHERE username='anonymous'

which looks legit to me, though I'm not really an SQL expert.

So maybe it's raising a warning every time I write to the
database? Why?  And more to the point, what is the warning --
shouldn't it be giving me some kind of message from MySQL?

Should I just stick the try-except code back in and forget
about it, or am I missing a step somewhere? Any ideas would
be much appreciated.

Thanks!
Terry

-- 
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Terry Hancock
hancock@anansispaceworks.com       
Anansi Spaceworks                 
http://www.anansispaceworks.com 
------------------------------------------------------