1 files changed, 6 insertions, 6 deletions
diff --git a/nixpkgs/pkgs/development/interpreters/python/sitecustomize.py b/nixpkgs/pkgs/development/interpreters/python/sitecustomize.py
index 72ce951328f1..d79a4696d8ea 100644
--- a/nixpkgs/pkgs/development/interpreters/python/sitecustomize.py
+++ b/nixpkgs/pkgs/development/interpreters/python/sitecustomize.py
@@ -21,9 +21,11 @@ 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
+# 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)
@@ -32,8 +34,6 @@ if not in_venv:
     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
+        # Sysconfig does not like it when sys.prefix is set to None
         sys.prefix = sys.exec_prefix = prefix
         site.PREFIXES.insert(0, prefix)