[ZODB-Dev] ZODB file never updated - import transaction fails...

[Chris McDonough]

Since your exception is happening during __del__ and since AFAIK no  
guarantees are made as to what will exist is sys.modules during any  
given object's __del__, it's maybe not suprising that you're getting  
this exception.  I don't know that this has anything to do with ZODB  
in particular.

The first thing I'd try to do is to move the cleanup code out of  
__del__ (and perhaps to a finally: after the line that creates the  
cache instead) and see if that helps.

- C

On Jul 29, 2006, at 9:40 AM, skip at pobox.com wrote:

>
> Matt Cowles has a DNS cache module with a patch for use with  
> SpamBayes.  It
> doesn't persist the data (just caches during the lifetime of the  
> run).  I'm
> trying to add persistence to that cache and wanting to use the same  
> database
> as the user selects for the main SpamBayes database, my first two  
> targets
> were anydbm and ZODB.  I'm having trouble with the ZODB setup.  It  
> seemed to
> work well at the start, but the database file is never updated when  
> I rerun
> my training script, so its not caching anything, and now everything  
> in the
> database has expired.  I've never used ZODB before.  The amount of  
> code is
> fairly small, so I'll just post it here in hopes someone can see  
> what I've
> done wrong.
>
> When opening the database it selects based on the user-preferred  
> filetype.
> For "zodb" it executes:
>
>     from ZODB import DB
>     from ZODB.FileStorage import FileStorage
>     self._zodb_storage = FileStorage(cachefile, read_only=False)
>     self._DB = DB(self._zodb_storage, cache_size=10000)
>     self._conn = self._DB.open()
>     root = self._conn.root()
>     self.caches = root.get("dnscache")
>     if self.caches is None:
>         # There is no classifier, so create one.
>         from BTrees.OOBTree import OOBTree
>         self.caches = root["dnscache"] = OOBTree()
>         self.caches["A"] = {}
>         self.caches["PTR"] = {}
>
> That gives the cache a caches attribute that looks like the  
> dictionary it
> uses in the no persistence case.
>
> When the cache is deleted, its __del__ method calls
>
>     self.close()
>
> which calls self._zodb_close():
>
>   def _zodb_close(self):
>       # Ensure that the db is saved before closing.  Alternatively, we
>       # could abort any waiting transaction.  We need to do  
> *something*
>       # with it, though, or it will be still around after the db is
>       # closed and cause problems.  For now, saving seems to make  
> sense
>       # (and we can always add abort methods if they are ever needed).
>       self._zodb_store()
>
>       # Do the closing.
>       self._DB.close()
>
> which calls self._zodb_store():
>
>   def _zodb_store(self):
>       import transaction
>       from ZODB.POSException import ConflictError
>       from ZODB.POSException import TransactionFailedError
>
>       try:
>           transaction.commit()
>       except ConflictError, msg:
>           # We'll save it next time, or on close.  It'll be lost if we
>           # hard-crash, but that's unlikely, and not a particularly  
> big
>           # deal.
>           if options["globals", "verbose"]:
>               print >> sys.stderr, "Conflict on commit.", msg
>           transaction.abort()
>       except TransactionFailedError, msg:
>           # Saving isn't working.  Try to abort, but chances are that
>           # restarting is needed.
>           if options["globals", "verbose"]:
>             print >> sys.stderr, "Store failed.  Need to restart.",  
> msg
>           transaction.abort()
>
> which seems to fail.  I get this message in the log:
>
>     Exception exceptions.ImportError: 'No module named transaction' in
>     <bound method cache.__del__ of <spambayes.dnscache.cache  
> instance at
>     0x11994b8>> ignored
>
> I can import transaction from the interpreter prompt just fine:
>
>     % python
>     Python 2.5b2 (trunk:50921, Jul 28 2006, 20:21:50)
>     [GCC 4.0.0 (Apple Computer, Inc. build 5026)] on darwin
>     Type "help", "copyright", "credits" or "license" for more  
> information.
>>>> import transaction
>>>> transaction.__file__
>     '/Users/skip/local/lib/python2.5/site-packages/transaction/ 
> __init__.pyc'
>>>> import ZODB
>>>> ZODB.__file__
>     '/Users/skip/local/lib/python2.5/site-packages/ZODB/__init__.pyc'
>
> I stuck a
>
>     print transaction.__file__
>
> after the import in _zodb_close and ran dnscache as a main.  It  
> prints out
>
>     /Users/skip/local/lib/python2.5/site-packages/transaction/ 
> __init__.pyc
>
> so I'm pretty sure I'm getting the same version of Python.  Any  
> idea why it
> would fail in one instance but not another?  The only thing I can  
> think of
> is that there are two ZODB databases opened at the same time in the  
> real use
> case, but only the one in the situation where I'm running the  
> dnscache test
> function.  Is there something about having two distinct ZODB  
> database files
> open I need to consider?
>
> Thanks,
>
> -- 
> Skip Montanaro - skip at pobox.com - http://www.mojam.com/
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