[Zope3-dev] Please, no bare 'except:' clauses!

[Jim Fulton]

Shane Hathaway wrote:
> R. David Murray wrote:
> 
>> On Mon, 11 Nov 2002, Barry A. Warsaw wrote:
>>
>>> But if the three main subsystems you outlined each defined their own
>>> base exception class (deriving from Exception), and application code
>>> made sure to catch only the derived classes, I think you could largely
>>> stil accomplish this goal.
>>
>>
>> [....]
>>
>>> except DatabaseError: # All ZODB/transactional errors (conflicts, etc)
>>>
>>> except ZopeError: # All Zope framework exceptions
>>>
>>> except AppError: # All application defined exceptions
>>>
>>> except Exception: # All Python exceptions
>>
>>
>>
>> But if you trap Exception, you are still trapping DatabaseErrors.
>> The goal was to have a way to trap everything (including 'python'
>> errors) *except* for DatabaseErrors.  And an enhancedment to
>> the except command wouldn't be enough, because what we want
>> to do is specify that DatabaseErrors can't be caught by a framework
>> that may not be Database-aware.
> 
> 
> I see a few options:
> 
> 1) Don't let DatabaseErrors be so special any more.  Currently, we want 
> ConflictErrors to propagate, in order to prevent inconsistent data from 
> being committed, and to give the app an opportunity to retry.  But 
> excessive exception catching ought not to be so catastrophic.  I think 
> any attempt to write or commit after a ConflictError has occurred should 
> result in another ConflictError, since the data being written is 
> generated from inconsistent data.  AFAICT this would eliminate the need 
> to make DatabaseErrors special, and would only change ZODB.

This is already the case.

Jim

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