[Python-Dev] ANNOUNCE: CapPython, an object-capability subset of Python

[Guido van Rossum]

How about Capt'n Python? :-)

Anyway, this is way cool. Looking forward to kicking the tires!

On Thu, Sep 18, 2008 at 1:33 PM, Terry Reedy <tjreedy at udel.edu> wrote:
> Mark Seaborn wrote:
>>
>> During the past couple of months I have been working on an
>> object-capability subset of Python - in other words, a restricted
>> execution scheme for sandboxing Python code.  It has been influenced
>> by other object-capability subset languages, such as Joe-E (a subset
>> of Java [1]), Caja/Cajita (subsets of Javascript [2]) and Caperl
>> (based on Perl [3]).  I'm calling it CapPython because the name
>> doesn't seem to have been taken yet. :-)
>
> No wonder ;-).  I like CapPy better, though there is a shareware screen
> capture program by that name. PyCap is taken.  CapThon is not.
>>
>> I believe it is now secure, so it seems like a good time to announce
>> it here!
>>
>> The basic idea behind CapPython is to enforce encapsulation by
>> restricting access to private attributes of objects.  This is achieved
>> through a combination of static checking and limiting access to unsafe
>> builtins and modules.
>>
>> Private attributes may only be accessed through "self" variables.
>> "Self" variables are defined as being the first arguments of functions
>> defined inside class definitions, with a few restrictions intended to
>> prevent these functions from escaping without being safely wrapped.
>
> What about functions defined outside class definitions and then attached as
> an attribute.  Prevented?
>
>> Private attribute names are those starting with "_".   Additionally,
>> "im_self", "im_func" and some other special cases are treated as
>> private attributes.
>
> In 3.0, unbound methods are gone and im_self and im_func are __self__ and
> __func__ attributes of method objects.
>
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-- 
--Guido van Rossum (home page: http://www.python.org/~guido/)