Python: fix virtualenv with Python 2

pkgs/development/python-modules/virtualenv/0001-Check-base_prefix-and-base_exec_prefix-for-Python-2.patch

@@ -0,0 +1,37 @@
+From 21563405d6e2348ee457187f7fb61beb102bb367 Mon Sep 17 00:00:00 2001
+From: Frederik Rietdijk <fridh@fridh.nl>
+Date: Sun, 24 May 2020 09:33:13 +0200
+Subject: [PATCH] Check base_prefix and base_exec_prefix for Python 2
+
+This is a Nixpkgs-specific change so it can support virtualenvs from Nix envs.
+---
+ src/virtualenv/discovery/py_info.py | 8 ++++++--
+ 1 file changed, 6 insertions(+), 2 deletions(-)
+
+diff --git a/src/virtualenv/discovery/py_info.py b/src/virtualenv/discovery/py_info.py
+index 6f12128..74e9218 100644
+--- a/src/virtualenv/discovery/py_info.py
++++ b/src/virtualenv/discovery/py_info.py
+@@ -51,13 +51,17 @@ class PythonInfo(object):
+         self.version = u(sys.version)
+         self.os = u(os.name)
+ 
++        config_vars = {} if sys.version_info.major is not 2 else sysconfig._CONFIG_VARS
++        base_prefix = config_vars.get("prefix")
++        base_exec_prefix = config_vars.get("exec_prefix")
++
+         # information about the prefix - determines python home
+         self.prefix = u(abs_path(getattr(sys, "prefix", None)))  # prefix we think
+-        self.base_prefix = u(abs_path(getattr(sys, "base_prefix", None)))  # venv
++        self.base_prefix = u(abs_path(getattr(sys, "base_prefix", base_prefix)))  # venv
+         self.real_prefix = u(abs_path(getattr(sys, "real_prefix", None)))  # old virtualenv
+ 
+         # information about the exec prefix - dynamic stdlib modules
+-        self.base_exec_prefix = u(abs_path(getattr(sys, "base_exec_prefix", None)))
++        self.base_exec_prefix = u(abs_path(getattr(sys, "base_exec_prefix", base_exec_prefix)))
+         self.exec_prefix = u(abs_path(getattr(sys, "exec_prefix", None)))
+ 
+         self.executable = u(abs_path(sys.executable))  # the executable we were invoked via
+-- 
+2.25.1
+

pkgs/development/python-modules/virtualenv/default.nix

@@ -43,6 +43,10 @@ buildPythonPackage rec {
     importlib-metadata
   ];
 
+  patches = lib.optionals (isPy27) [
+    ./0001-Check-base_prefix-and-base_exec_prefix-for-Python-2.patch
+  ];
+
   meta = {
     description = "A tool to create isolated Python environments";
     homepage = "http://www.virtualenv.org";