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

[Yuppie]

Hi!


seb bacon wrote:
> Yuppie wrote:
>> 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.

You meant the other way round? 'except Exception' doesn't catch string 
exceptions, only class exceptions.

>> 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.

Something like this?

   class CMFError(StandardError):
     ...
   class MembershipError(CMFError):
     ...
   class MetadataError(CMFError):
     ...
   ...

> 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.

If this is the way to go, I'd like to start using a new 
CMFCoreExceptions.py for the new code I add in MembershipTool.py.

Updating the existing code could be done later. I have no idea how to 
achieve backwards compatibility, but I think this should be done anyway.


Cheers,
	Yuppie