New submission from Arnaud Porterie:
In the Data Model section of the documentation regarding descriptors
invokations
(http://docs.python.org/2/reference/datamodel.html#invoking-descriptors), it is
said:
Note that descriptors are only invoked for new style objects or classes
(ones that subclass object() or type()).
However, it seems this restriction isn't enforced in practice:
Python 2.7.4 (default, May 16 2013, 13:28:03)
[GCC 4.2.1 Compatible Apple Clang 4.0 ((tags/Apple/clang-421.0.60))] on
darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> class Desc(object):
... def __get__(self, obj, cls):
... return 'test'
...
>>> class A: # Not inheriting object here
... desc = Desc()
...
>>> A().desc
'test'
I dived into CPython's code and saw no trace of a test for new-style classes in
the descriptor invokation code path (down in classobject.c / instance_getattr2).
Unfortunately, fixing this behavior doesn't seem trivial as class methods
appear to be implemented as descriptor themselves. In other words, and from my
understanding, restricting descriptor invokation to new-style objects and
classes would prevent method calls on old-style classes.
----------
components: Interpreter Core
files: desc.py
messages: 189896
nosy: icecrime
priority: normal
severity: normal
status: open
title: Descriptors get invoked in old-style objects and classes
type: behavior
versions: Python 2.7
Added file: http://bugs.python.org/file30356/desc.py
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Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue18047>
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