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"""
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 or virtualenv.
# For Python 3 we check whether our `base_prefix` is different from our current `prefix`.
# For Python 2 we check whether the non-standard `real_prefix` is set.
# https://stackoverflow.com/questions/1871549/determine-if-python-is-running-inside-virtualenv
in_venv = (sys.version_info.major == 3 and sys.prefix != sys.base_prefix) or (sys.version_info.major == 2 and hasattr(sys, "real_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:
# Sysconfig does not like it when sys.prefix is set to None
sys.prefix = sys.exec_prefix = prefix
site.PREFIXES.insert(0, prefix)
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