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

[MRAB]

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"?
> 
Here's my guess:

Some objects have a fixed (and possibly empty) set of attributes.
Attempting to add a new attribute or get a non-existent attribute raises
an AttributeError.

Other objects, such as types (are there any that aren't types?), don't
have attributes at all. Attempting to add or get an attribute raises a
TypeError.