NameError vs AttributeError
Ethan Furman
ethan at stoneleaf.us
Wed Aug 1 11:53:40 EDT 2012
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.
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