Re: PYTHONPATH issue explanation

[iyzsong@member.fsf.org (宋文武)]

Hartmut Goebel <h.goebel@crazy-compilers.com> writes:

Hello,

> Hi,
>
> given the ongoing discussion around Python show that my explanation was
> not good enough. I'll try to summarize and give more background.

Thanks for the explanations and this one!

So I have more understanding of it and ideas...

>
> With regard to Python, guix currently has a major issue, which my
> proposals are addressing. There are other issues (like naming the
> executables, the "wrapper" script", etc.) which are not addressed
> here.
> [...]

Okay, the "major issue" is that we're using "PYTHONPATH", which will add
entries into "sys.path" before builtin ones.  It's semantically wrong
and may (or had?) cause issues.


> Part 3 of my analysis lists three solutions for this, where only number
> 2 and 3 are "good choices".

Option 2, "GUIX_PYTHONHOME_X_Y" can not be used in the build-system
unless we make a union of python inputs, so I think we should go for 1
and optional (later) add 3 too:

- "GUIX_PYTHON_X_Y_SITE_PACKAGES" (X.Y is not a valid env identifier
  in bash) is necessary for the "build" environment.

  We don't make a union of all the inputs in the "build" environment, so
  a PATH (contains multiples directories) like env have to be used to
  let python find all its "site-packages" from inputs.

  > Drawbacks: This might break Python appications expecting
  > site-packages to be below sys.prefix.

  We have a patch named "python-2.7-site-prefixes.patch" seems to handle
  this, maybe we should do it for python3 too?


- Avoid any environment variable for the "profile" environment.

  We have a union "profile" for all the python packages, so environment
  variables can be totally avoided with the help of "venv".

  > We could avoid GUIX-PYTHONHOME[23] if we stop resolving the symlinks
  > at the correct point in iteration.

  This is exactly what "venv" does!  We only need to make the "profile"
  a "venv" for python.  For python3, a simple "pyvenv.cfg" file is
  enough, for python2 I guess we have to make a union or copy files like
  what "virtualenv" does.


I plan to implement option 1 by adding a "sitecustomize.py" (better
than modify "site.py") into the python packages, and modify
"search-path-specification" to use "GUIX_PYTHON_X_Y_SITE_PACKAGES".

How's that sound?