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Thu Aug 5 09:45:28 CEST 2004 · https://mail.python.org/pipermail/python-dev/2004-August/046852.html

Paul Prescod wrote:
> Greg Ewing wrote:
> 
>> ...
>>
>>> I don't really think that "raise 42"
>>> ought to be acceptable, but I don't know how to prevent it
>>
>>
>>
>> Maybe we need to think more deeply about *why* it shouldn't be
>> acceptable. If we can figure out exactly what the criterion should be,
>> maybe we can think of a reasonable way of testing for it.
> 
> 
> Exceptions naturally form a hierarchy. At the same time, inheritance of 
> behaviour among exceptions is seldom necessary. Therefore, exceptions 
> inherit from each other in order to build a classification system, not 
> to share code. 

I wouldn't say that: exceptions can have error handlers, callbacks,
inherited attributes, etc. etc. and you can put these to good
use in your application.

> This is the opposite of the traditional reasons for 
> classes inheriting from other classes in Python. This is why it seems 
> "unpythonic" to require exceptions to be single-rooted.

I don't know what should be "unpythonic" about having a single
root for exceptions. Would someone care to explain ?

To me ...

try:
     ...
except Exception, errobj:
     # catches all exceptions
     pass

... is the most natural way of using that single root (and it already
works great today).

> But having a proper classification system is exactly what is required to 
> allow robust, modular code that catches the right exceptions under the 
> right circumstances and responds in the right way. So it is pythonic 
> after all.
 >
> In a few senses the _current model_ is unpythonic. There is no catch-all 
> root so you have to use a "bare" except to catch every exception type. 
> This makes it hard to introspect on the caught object. But introspection 
> is the MOST IMPORTANT THING when you are catching all exceptions 
> (because you should be logging the exception or something).

-- 
Marc-Andre Lemburg
eGenix.com

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