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

[Terry Reedy]

Seo Sanghyeon wrote:
> Exception for setting attributes of built-in type differs between
> CPython and IronPython. This is not purely theoretical, as
> zope.interface tries to set Implements declaration as __implemented__
> attribute of built-in type object, and excepts TypeError.
> 
> Python 2.6.1
>>>> object.flag = True
> TypeError: can't set attributes of built-in/extension type 'object'
> 
> IronPython 2.6
>>>> object.flag = True
> AttributeError: 'object' object has no attribute 'flag'
> 
> I was surprised that CPython raises TypeError. Library Reference seems
> to mention it here:
> 
> exception AttributeError
> Raised when an attribute reference or assignment fails. (When an
> object does not support attribute references or attribute assignments
> at all, TypeError is raised.)
> http://docs.python.org/library/exceptions.html
> 
> What does it mean that "an object does not support attribute
> references or attribute assignments at all"?

I see it as slightly ambiguous:
1. It neither supports references nor assignments.
2. It either does not support reference or it does not support assignments.

1 could hardly apply any more, certainly to built-ins since everything 
now has attributes.  2 covers object, so if that is meant, then 
TypeError is appropriate.

Or were you unclear about 'at all', which means 'never'?

Terry Jan Reedy