Viewing the final SQL?

[Peter Bowyer]

I'm just starting with Python, and would like to know how I can view the SQL after interpolation? I'm fighting this error message:

Traceback (most recent call last):
File "feedsloader.py", line 151, in ?
main()
File "feedsloader.py", line 145, in main
feeder.process(feed)
File "feedsloader.py", line 77, in process
(etag, modified, data.status, feed['feed_id']))
File "/usr/lib/python2.4/site-packages/MySQLdb/cursors.py", line 137, in execute
self.errorhandler(self, exc, value)
File "/usr/lib/python2.4/site-packages/MySQLdb/connections.py", line 33, in defaulterrorhandler
raise errorclass, errorvalue
_mysql_exceptions.OperationalError: (1205, 'Lock wait timeout exceeded; Try restarting transaction')

despite not using transactions or threading. I am hoping that viewing the SQL as the database sees it may give some pointer to the problem.

[Eric Huss]

Would you be willing to expose a method that would provide a string after the interpolation? In my case, I'd rather do that than do it at query-time. I actually just want to call connection.literal(), but the docstring says not to do that. ;)

[Peter Bowyer]

I fixed the error (I hadn't realised I needed to commit() the changes, as I've never needed to in PHP), but the original question still stands.

[Andy Dustman]

PHP was likely using auto-commit mode, or using non-transactional tables, so you weren't getting transactions at all.

There's not a built-in way to see the raw SQL statements before they are issued. However, you could probably do something like this (untested and pre-coffee):

class DebugCursor(MySQLdb.Cursor):

def _query(self, q):
    import sys
    print >> sys.stderr, q
    return self._do_query(q)

...

c = db.cursor(DebugCursor)

perform query as normal

If you aren't getting exceptions, you can also just look at c._executed for the last raw executed query.