Steven D'Aprano wrote:
Not that I don't believe you (I do!) but could you demonstrate for the record?
I posted a demonstration of this earlier in this thread. The key thing is the __subclasses__() method of a class. You can start with any object, work your way up the base class chain to object, and then use __subclasses__() to get to any builtin class in the system, including file. There was a sandboxing scheme put forward a while back which involves vetting the code and disallowing the use of any double-underscore attribute names. With a suitably censored set of builtin functions, this prevents the use of the __subclasses__ hack, as well as some other potential lines of attack. As far as I know, nobody managed to break it at the time, but it probably hasn't been tested much in the real world, if at all, so I probably wouldn't recommend using it for anything critical. -- Greg -- http://mail.python.org/mailman/listinfo/python-list
