[Python-Dev] [Python-checkins] r86566 - in python/branches/py3k: Doc/glossary.rst Doc/library/inspect.rst Lib/inspect.py Lib/test/test_inspect.py Misc/NEWS Misc/python-wing4.wpr (original) (raw)

Michael Foord fuzzyman at voidspace.org.uk
Sat Nov 20 17:06:59 CET 2010

On 20/11/2010 16:01, Nick Coghlan wrote:

On Sun, Nov 21, 2010 at 1:29 AM, Michael Foord <fuzzyman at voidspace.org.uk> wrote:

Can you give an example of code in a metaclass that may be executed by getattrstatic? It's not that I don't believe you I just can't think of an example. Looking up the class and the mro are the only two examples I can think of (klass.mro and instance.class - and they are noted in the docs?) but aren't metaclass specific. The description heavily implies that arbitrary Python code won't be executed by calling getattrstatic, and that isn't necessarily true. It's almost certain to be true in the case when the metaclass is type, but can't be guaranteed otherwise.

Given the way that member lookups are done by getattr_static I don't think any assumptions about the metaclass are made. I'm happy to be proven wrong (but would rather fix it than document it as an exception). (Actually we assume the metaclass doesn't use slots, but only because it isn't possible for a metaclass to use slots.)

The retrieval of class is a normal lookup on the object, so it can trigger all of the things getattrstatic is trying to avoid (unavoidable if you want to support proxy classes at all), and the lookup of mro invokes all of those things on the metaclass.

class and mro lookup are noted in the docs as being exceptions. We could actually remove the class lookup from the list of exceptions by using type(...) instead of obj.class.

I'll see if I'm still of the same opinion after I sleep on it, but my first impression of the docs was that they slightly oversold the strength of the "doesn't execute arbitrary code" aspect of the new function. The existing caveats were all relating to when getattr() and getattrstatic() might give different answers, while the additional caveats I was suggesting related to cases where arbitrary code may still be executed. I'm happy to change the wording to make the promise less strong.

All the best,

Michael

Cheers, Nick.

--

http://www.voidspace.org.uk/

READ CAREFULLY. By accepting and reading this email you agree, on behalf of your employer, to release me from all obligations and waivers arising from any and all NON-NEGOTIATED agreements, licenses, terms-of-service, shrinkwrap, clickwrap, browsewrap, confidentiality, non-disclosure, non-compete and acceptable use policies (”BOGUS AGREEMENTS”) that I have entered into with your employer, its partners, licensors, agents and assigns, in perpetuity, without prejudice to my ongoing rights and privileges. You further represent that you have the authority to release me from any BOGUS AGREEMENTS on behalf of your employer.

More information about the Python-Dev mailing list