pypy alongside cpython + base/interpreter for noarch:python packages

[mbargull]

In reference to
@mattip in conda-forge/conda-forge.github.io#867 (comment):

Would a user ever get into a situation where they have two interpreters in the same conda environment?

Will Conda packages for CPython and PyPy themselves have path conflicts, e.g., both having bin/python or lib/pythonX.Y/some-file? IIRC, PyPy uses a different lib/some-thing path, right?

If there are no conflicts, we could potentially let them be installable side by side.

How would conda handle its noarch: python packages for PyPy? Currently, it uses python.exe or bin/pythonX.Y. Either the pypy package, or the python=*=pypy package should provide those binaries. If we put them into the python package, we could do the same for cpython and ensure exclusivity. (I guess this may put off some people since cpython wouldn't be considered "complete" then. Well, I'm just putting down thoughts as them come right now and still lack a view of the whole picture...)

[mattip]

IIRC, PyPy uses a different lib/some-thing path, right?

That is a decision for conda to make. As packaged in the PyPy-provided tarballs, PyPy's stdlib and site-packages paths are different, but not for any good reason. Typically packages like debian, arch modify this as they wish. If conda wishes to put the two iplementaitons into the same environment they should ensure the layouts are different, and that the typical symlink of bin/pypy -> bin/python is not created.
I would advise against it as "too complicated" but I don't know how sensitive users are to disk space

[mattip]

Would this design be valid for building feedstocks that use c-extension modules like NumPy and lxml? They cannot be shared across implementations.

[msarahan]

yes. Those packages would use the python-devel package shown in the recipe here. That would add a runtime dependency on either pypy or cpython to prevent ambiguity and problems. It might need tweaking beyond the example here, but the rough idea here should work.

[mbargull]

[...] PyPy's stdlib and site-packages paths are different, but not for any good reason. Typically packages like debian, arch modify this as they wish.

Good to know, thanks!

[...] I would advise against it as "too complicated"

👍 TBH, that was what I anticipated to hear. IMHO, there is not too much value in having CPython and PyPy in the same environment.
(I mean, conda-forge and Anaconda don't even support running a Python 2 interpreter in the same environment as a Version 3 one, i.e., we don't offer separate python2 packages -- so not offering CPython and PyPy in the same env should not come as too much of a surprise for the user.)