[Python-Dev] Exception for setting attributes of built-in type

[Nick Coghlan]

Benjamin Peterson wrote:
> 2009/6/15 Nick Coghlan <ncoghlan at gmail.com>:
>> Guido van Rossum wrote:
>>> In general, CPython isn't always consistent in raising AttributeError
>>> and TypeError when it comes to such policy issues: there are various
>>> places that raise TypeError in typeobject.c (and probably elsewhere)
>>> that simply forbid setting a specific attribute (another example is
>>> __name__).
>> We're pretty inconsistent when it comes to looking up special methods as
>> well - those that are looked up through dedicated slots in abstract.c
>> usually raise TypeError, while those that are looked up via a PyType
>> method usually raise AttributeError.
> 
> What's a PyType method?

I was misremembering - for some reason I thought:
a) _PyObject_LookupSpecial was a PyType method
b) That it raised AttributeError itself instead of letting the caller
decide what error to raise

It's still the case that (e.g.) special_lookup() in ceval.c raises an
AttributeError, as do special method lookups from Python of the form
"type(obj).__method__(obj)".

Whether CPython raises TypeError or AttributeError when it comes to
special methods is really pretty arbitrary rather than a matter of any
grand design.

Cheers,
Nick.

P.S. If anyone feels like digging into the archives, the last time I can
recall this topic coming up is when I was concerned about the original
with statement implementation raising AttributeError rather than
TypeError when it couldn't find an __enter__ or __exit__ method. Guido
chimed in then (as now) to say that either exception was fine.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia
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