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[Python-ideas] A python bridge between versions

M.-A. Lemburg mal at egenix.com
Fri Feb 28 10:16:34 CET 2014 
On 28.02.2014 01:48, James Powell wrote:
> On 02/27/2014 06:51 PM, M.-A. Lemburg wrote:
>> On 28.02.2014 00:26, ian o wrote:
>>>  [... Embed Python 2 in Python 3 ...]
>>>
>>>  Thoughts or criticisms?
> 
>> There's a catch here: Python 2 and Python 3 use the same C APIs,
>> so you'd have to separate the two in some way to make both live
>> in the same process.
> 
> I actually have a working embedding of Python 3 into Python 2, which
> I've presented at a few conferences, most recently at PyData London this
> past weekend.
> 
> It's just a C-extension module that embeds a Python 3
> PyRun_SimpleString. I haven't gotten around to building a shim to
> interact with Python 3 objects in Python 2 (and this would require a
> little bit of sophistication to handle GIL, GC, &c. issues.)
> 
> Still, it's a working example of Python 2 and Python 3 running in the
> same process.

Interesting :-) Do you have some pointers to slides or videos ?

I'm been thinking of doing something like this but the other way
around - embed Python2 in Python3. When starting to brainstorm
that idea, I quickly ended up postponing the idea again due to
problems with C extension linking, dual interpreter environments,
object interfacing between the two worlds, having two separate
exception class trees, two sets of basic types/classes, two GILs,
etc.

The linking part was the most important to me, since being able
to use Python 2 extensions would be my main reason to stick with
Python 2 for some more time.

>> It's not impossible, but it can potentially ruin the idea, since
>> C extensions for both Python versions will have to link the right
>> set of C APIs.
> 
> I did this by "source filtering" - i.e., rewriting exported symbols to
> allow linking against both interpreters. This is admittedly a very
> primitive approach and limits its use in production.
> 
> I recently put some time into trying to redo this embedding using cffi
> and worked through a few problems in this approach with one of the
> cython/numba developers. I haven't gotten anything working yet. I may
> need to ask Xzibit if he has any suggestions.
> 
> I don't know if this idea has any serious applications. It's definitely
> been a fun toy for presenting ideas about interpreter embedding and
> exploring certain facets of CPython!
> 
> Cheers,
> James Powell
> 
> follow: @dontusethiscode + @nycpython
> attend: nycpython.org
> read:   seriously.dontusethiscode.com

Cheers,
-- 
Marc-Andre Lemburg
eGenix.com

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