limited python virtual machine

[Alex Martelli]

Stephen Thorne <stephen.thorne at gmail.com> wrote:

> On Sat, 29 Jan 2005 08:53:45 -0600, Skip Montanaro <skip at pobox.com> wrote:
> > 
> >     >> One thing my company has done is written a ``safe_eval()`` that uses
> >     >> a regex to disable double-underscore access.
> > 
> >     Alex> will the regex catch getattr(object,
> >     Alex> 'subclasses'.join(['_'*2]*2)...?-)
> > 
> > Now he has two problems. ;-)
> 
> I nearly asked that question, then I realised that 'getattr' is quite
> easy to remove from the global namespace for the code in question, and
> assumed that they had already thought of that.

OK then -- vars(type(object)) is a dict which has [[the unbound-method
equivalent of]] object.__subclasses__ at its entry for key
'__subclasses__'.  Scratch 'vars' in addition to 'getattr'.  And 'eval'
of course, or else building up the string 'object.__subclasses__' (in a
way the regex won't catch) then eval'ing it is easy.  I dunno, maybe I'm
just being pessimistic, I guess...


Alex