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Date: Wed, 01 Aug 2012 08:53:40 -0700
From: Ethan Furman <ethan@stoneleaf.us>
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Subject: Re: NameError vs AttributeError
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Terry Reedy wrote:
> On 7/31/2012 4:49 PM, Chris Kaynor wrote:
>> On Tue, Jul 31, 2012 at 1:21 PM, Terry Reedy wrote:
>>> Another example: KeyError and IndexError are both subscript errors,
>>> but there is no SubscriptError superclass, even though both work
>>> thru the same mechanism -- __getitem__.  The reason is that there is
>>> no need for one. In 'x[y]', x is usually intented to be either a
>>> sequence or mapping, but not possibly both. In the rare cases when
>>> one wants to catch both errors, one can easily enough. To continue
>>> the example above, popping an empty list and empty set produce
>>> IndexError and KeyError respectively:
>>>
>>>    try:
>>>      while True:
>>>        process(pop())
>>>    except (KeyError, IndexError):
>>>      pass  # empty collection means we are done
>>>
>> There is a base type for KeyError and IndexError: LookupError.
>>
>> http://docs.python.org/library/exceptions.html#exception-hierarchy
> 
> Oh, so there is. Added in 1.5 strictly as a never-directly-raised base 
> class for the above pair, now also directly raised in codecs.lookup. I 
> have not decided if I want to replace the tuple in the code in my book.

I think I'd stick with the tuple -- LookupError could just as easily 
encompass NameError and AttributeError.