bug#52269: [core-updates-frozen] sitecustomize.py does not honor .pth files

[Maxim Cournoyer]

Hello,

Lars-Dominik Braun <lars@6xq.net> writes:

> Hi Maxim,
>
>> +if not matching_sites:
>> +    exit(0)
> are you sure about using `exit()` here? sitecustomize.py is imported
> during startup and this would simply quit the Python interpreter if
> GUIX_PYTHONPATH is not set, wouldn’t it? (Can’t test the change
> unfortunately, because it’s a massive rebuild.)

You can test it by placing the new sitecustomize.py file in the current
directory, and then:

$ guix shell python-wrapper python-pdbpp

[env]$ $ PYTHONPATH=. GUIX_PYTHONPATH= python sample.py

where sample.py contains something like:

--8<---------------cut here---------------start------------->8---
__import__("pdb").set_trace()

print('hello')
--8<---------------cut here---------------end--------------->8---

Indeed, when GUIX_PYTHONPATH is unset or matching_sites is empty, it
exit with 0 as you expected:

--8<---------------cut here---------------start------------->8---
$ PYTHONPATH=. GUIX_PYTHONPATH= python sample.py
Fatal Python error: init_import_site: Failed to import the site module
Python runtime state: initialized
Traceback (most recent call last):
  File 
"/gnu/store/p5fgysbcnnp8b1d91mrvjvababmczga0-python-3.9.6/lib/python3.9/site.py",
 line 589, in <module>
    main()
  File 
"/gnu/store/p5fgysbcnnp8b1d91mrvjvababmczga0-python-3.9.6/lib/python3.9/site.py",
 line 582, in main
    execsitecustomize()
  File 
"/gnu/store/p5fgysbcnnp8b1d91mrvjvababmczga0-python-3.9.6/lib/python3.9/site.py",
 line 521, in execsitecustomize
    import sitecustomize
  File "/home/maxim/proj/kinova/kts_robot/sitecustomize.py", line 52, in 
<module>
    exit(0)
  File 
"/gnu/store/p5fgysbcnnp8b1d91mrvjvababmczga0-python-3.9.6/lib/python3.9/_sitebuiltins.py",
 line 26, in __call__
    raise SystemExit(code)
SystemExit: 0
--8<---------------cut here---------------end--------------->8---

After the proposed change:

--8<---------------cut here---------------start------------->8---
[env]$ PYTHONPATH=. GUIX_PYTHONPATH= python sample.py
> /home/maxim/proj/kinova/kts_robot/sample.py(5)<module>()
-> print('hello')
--8<---------------cut here---------------end--------------->8---

There's no longer pdbpp because of clearing GUIX_PYTHONPATH but at least
it doesn't crash :-).

>> +# Move the entries that were appended to sys.path in front of Python's own
>> +# site-packages directory.  This enables Guix packages to override Python's
>> +# bundled packages, such as 'pip'.
>> +python_site_index = sys.path.index(python_site)
>> +new_site_start_index = sys.path.index(matching_sites[0])
>> +if python_site_index < new_site_start_index:
>> +    sys.path = (sys.path[:python_site_index]
>> +                + sys.path[new_site_start_index:]
>> +                + sys.path[python_site_index:new_site_start_index])
> This is unrelated to the pdb issue, right? I see that it’s necessary
> right now, but as suggested in #46848 I’d prefer unbundling
> setuptools/pip from python. (I’ll send a v3 of the patchset at some
> point.)

Previously the Guix-provided paths were directly spliced at the right
location; now using 'site.addsitedir' simply appends them, which
requires manual fiddling afterward.

I agree that after it's un-bundled it shouldn't be necessary anymore, but
let's keep this change for core-updates along work on the 517
python-build-system (I'll try having a look to it after the next release
it out -- ping me otherwise).

Thank you,

Maxim

0001-sitecustomize.py-Honor-.pth-files.patch
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