Python: Difference between revisions

@@ Line 43: / Line 43: @@
 </syntaxhighlight>
+=== Emulating virtualenv with nix-shell ===
+In some cases virtualenv fails to install a library because it requires patching on NixOS (example 1, example 2, general issue). In this cases it is better to replace those libraries with ones from Nix.
+Let's say, that nanomsg library fails to install in virtualenv. Then write a `default.nix` file:
+<syntaxhighlight lang="nix">
+let pkgs = import <nixpkgs> {};
+     nanomsg-py = .... build expression for this python library;
+in pkgs.stdenv.mkShell {
+  buildInputs = [
+    pkgs.pythonPackages.pip
+    nanomsg-py
+  ];
+  shellHook = ''
+            alias pip="PIP_PREFIX='$(pwd)/_build/pip_packages' \pip"
+            export PYTHONPATH="$(pwd)/_build/pip_packages/lib/python2.7/site-packages:$PYTHONPATH"
+            unset SOURCE_DATE_EPOCH
+  '';
+}
+</syntaxhighlight>
+After entering the environemnt with `nix-shell`, you can install new python libraries with dump `pip install`, but nanomsg will be detected as installed.
 === conda ===