push sheeet

pkgs/development/interpreters/python/sitecustomize.py

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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)