nixpkgs/pkgs/development/interpreters/python/sitecustomize.py
Frederik Rietdijk 7447fff95a
Fix sys.prefix in case of a Nix env
The prefix will now be correct in case of Nix env.

Note, however, that creating a venv from a Nix env still does not function. This does not seem to be possible
with the current approach either, because venv will copy or symlink our Python wrapper. In case it symlinks
(the default) it won't see a pyvenv.cfg. If it is copied I think it should function but it does not...
2020-03-14 21:39:32 +00:00

40 lines
1.5 KiB
Python

"""
This is a Nix-specific module for discovering modules built with Nix.
The module recursively adds paths that are on `NIX_PYTHONPATH` to `sys.path`. In
order to process possible `.pth` files `site.addsitedir` is used.
The paths listed in `PYTHONPATH` are added to `sys.path` afterwards, but they
will be added before the entries we add here and thus take precedence.
Note the `NIX_PYTHONPATH` environment variable is unset in order to prevent leakage.
Similarly, this module listens to the environment variable `NIX_PYTHONEXECUTABLE`
and sets `sys.executable` to its value.
"""
import site
import sys
import os
import functools
paths = os.environ.pop('NIX_PYTHONPATH', None)
if paths:
functools.reduce(lambda k, p: site.addsitedir(p, k), paths.split(':'), site._init_pathinfo())
# Check whether we are in a venv.
# Note Python 2 does not support base_prefix so we assume we are not in a venv.
in_venv = sys.version_info.major == 3 and sys.prefix != sys.base_prefix
if not in_venv:
executable = os.environ.pop('NIX_PYTHONEXECUTABLE', None)
prefix = os.environ.pop('NIX_PYTHONPREFIX', None)
if 'PYTHONEXECUTABLE' not in os.environ and executable is not None:
sys.executable = executable
if prefix is not None:
# Because we cannot check with Python 2 whether we are in a venv,
# creating a venv from a Nix env won't work as well with Python 2.
# Also, note that sysconfig does not like it when sys.prefix is set to None
sys.prefix = sys.exec_prefix = prefix
site.PREFIXES.insert(0, prefix)