[Python-Dev] Exception for setting attributes of built-in type (original) (raw)

MRAB python at mrabarnett.plus.com
Mon Jun 15 00:42:56 CEST 2009

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.

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