[Python-Dev] Adding a builtins parameter to eval(), exec() and __import__().

[Mark Shannon]

Jim J. Jewett wrote:
> 
> http://mail.python.org/pipermail/python-dev/2012-March/117395.html
> Brett Cannon posted:
> 
> [in reply to Mark Shannon's suggestion of adding a builtins parameter
> to match locals and globals]
> 
>> It's a mess right now to try to grab the __import__()
>> implementation and this would actually help clarify import semantics by
>> saying that __import__() for any chained imports comes from __import__()s
>> locals, globals, or builtins arguments (in that order) or from the builtins
>> module itself (i.e. tstate->builtins).
> 
> How does that differ from today?

The idea is that you can change, presumable restrict, the builtins
separately from the globals for an import.

> 
> If you're saying that the locals and (module-level) globals aren't
> always checked in order, then that is a semantic change.  Probably
> a good change, but still a change -- and it can be made indepenently
> of Mark's suggestion.
> 
> Also note that I would assume this was for sandboxing, 

Actually, I just think it's a cleaner implementation,
but sandboxing is a good excuse :)

 > and that
> missing names should *not* fall back to the "real" globals, although
> I would understand if bootstrapping required the import statement to
> get special treatment.
> 
> 
> (Note that I like Mark's proposed change; I just don't see how it
> cleans up import.)

I don't think it cleans up import, but I'll defer to Brett on that.
I've included __import__() along with exec and eval as it is a place 
where new namespaces can be introduced into an execution.
There may be others I haven't though of.

Cheers,
Mark.