PyPy and RPython

sarvi sarvilive at
Fri Sep 3 11:07:27 CEST 2010

Well then, wouldn't it make sense for PyPy to use Shedskin and its
definition of Restricted Python?

I have heard repeatedly that PyPy RPython is very difficult to use.
Then why isn't PyPy using Shedskin to compile its PyPy-Jit?


On Sep 2, 11:59 pm, John Nagle <na... at> wrote:
> On 9/2/2010 10:30 PM, sarvi wrote:
> > On Sep 2, 2:19 pm, John Nagle<na... at>  wrote:
> >> On 9/2/2010 1:29 AM, sarvi wrote:
> >>> When I think about it these restrictions below seem a very reasonable
> >>> tradeoff for performance.
> >>      Yes.
> >>> And I can use this for just the modules/sections that are performance
> >>> critical.
> >>      Not quite.  Neither Shed Skin nor RPython let you call from
> >> restricted code to unrestricted code.  That tends to happen
> >> implicitly as objects are passed around.  It's the global
> >> analysis that makes this work; when you call something, you
> >> need to know more about it than how to call it.
> > It should technically be possible to allow Python to call a module
> > written in RPython?
>     The problem is that, in a language where everything is an object,
> everything you call calls you back.
>     The basic performance problem with CPython comes from the fact
> that it uses the worst-case code for almost everything.  Avoiding
> that requires global analysis to detect the places where the code
> clearly isn't doing anything weird and simpler code can be used.
> Again, look at Shed Skin, which represents considerable progress
> made by one guy. With more resources, that could be a very
> good system.
>                                 John Nagle

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