[Python-Dev] Proposed resolutions for open PEP 343 issues (original) (raw)
Nick Coghlan ncoghlan at gmail.com
Tue Oct 25 23:55:15 CEST 2005
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Guido van Rossum wrote:
On 10/25/05, Nick Coghlan <ncoghlan at gmail.com> wrote:
Almost there - this is the only issue I have left on my list :) [,,,]
Why are you so keen on TypeError? I find AttributeError totally appropriate. I don't see symmetry with for-loops as a valuable property here. AttributeError and TypeError are often interchangeable anyway. The reason I'm keen on TypeError is because 'abstract.c' uses it consistently when it fails to find a method to support a requested protocol. Hm. abstract.c well predates the new type system. Slots and methods weren't really unified back then, so TypeError made obvious sense at the time.
Ah, I hadn't considered that, because I never made significant use of any Python versions before 2.2.
Maybe there's a design principle in there somewhere:
Failed duck-typing -> AttributeError (or TypeError for complex checks) Failed instance or subtype check -> TypeError
Most of the functions in abstract.c handle complex protocols, so a simple attribute error wouldn't convey the necessary meaning. The context protocol, on the other hand, is fairly simple, and an AttributeError tells you everything you really need to know.
Cheers, Nick.
-- Nick Coghlan | ncoghlan at gmail.com | Brisbane, Australia
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