[Python-Dev] Reviving restricted mode?

[P.J. Eby]

At 07:56 PM 2/22/2009 -0800, Guido van Rossum wrote:
>On Sun, Feb 22, 2009 at 7:39 PM, P.J. Eby <pje at telecommunity.com> wrote:
> > Just a question, but, if you just need a pure-python restricted environment
> > for App Engine, why not just use the RestrictedPython package (i.e.,
> > http://pypi.python.org/pypi/RestrictedPython )?
>
>How does that work? Remember, app engine doesn't support certain
>things, and bytecode manipulations (if that's what RestrictedPython
>does) are one of the unsupported things.

It doesn't modify bytecode, it modifies an AST.  It basically 
replaces prints, and attribute/item read/writes with function 
calls.  Unfortunately, it does this AST modification by running as a 
traversal against the stdlib compiler package's AST, not a modern 
AST.  So, I suppose it might not be usable as-is on app engine.

It does, however, have the advantage of having been used in Zope for 
oh, six or seven years now?  ISTM that it first came out around the 
same time as Python 2.3, and the latest version just dropped support 
for Python 2.1 and 2.2.  So, if you want something that wasn't thrown 
together in an afternoon, it might be a good thing to take a look at.  ;-)


>The other reason I can think of is that Tav is a capabilities purist. :-)

You can implement capabilities on top of RestrictedPython; it's 
simply a policy-neutral enforcement framework.