[Zope-CMF] [dev] some questions regarding Exceptions

[seb bacon]

Yuppie wrote:
> Hi!
> 
> 
> Today I did have a closer look at Exception handling in CMF. These are 
> my questions:
> 
> 
> 1.) document_edit.py, metadata_edit.py and newsitem_edit.py in 
> CMFDefault are using this pattern:
> 
> try:
>     context.edit( ...
>     context.REQUEST.RESPONSE.redirect( ...
> except Exception, msg:
>     context.REQUEST.RESPONSE.redirect( ...
> 
> Am I right that these excepts also catch ConflictErrors, what's a Bad 
> Thing in general and especially with edit methods?

Yes, definitely.  In general it's a Bad Thing to catch all Exceptions 
without exception, because the "swallow everything" approach masks 
problems in an unhelpful way.  However, I guess these scripts are 
written as they are precisely so they can catch the string exceptions 
you mention.

> 2.) There are still many string exceptions in CMF. All the others are 
> not accessible TTW.
> 
> What would be the right way to resolve this?
> 
> We could use allow_module() and allow_class(). I guess in that case all 
> Exceptions should be in one module. Something like CMFCoreExceptions.py?

I like that idea.  If we design a core set of exceptions well, then 
folks can subclass them for their own needs and they'll still be caught 
by generic scripts.

> Or are there some CMF Exceptions that shouldn't be accessible TTW?

I don't see why you shouldn't be able to catch all exceptions TTW.

> Other thoughts?

The big blocker I can see is that achieving backwards compatibility 
could be a struggle.  I'm not sure about this though, someone would have 
to do a brief audit I guess.

Seb