Add nix cmake-init with temporary venv dir

cmake-init.nix

@@ -0,0 +1,42 @@
+{ pkgs ? import <nixpkgs> {}
+}:
+let
+  pythonPackages = pkgs.python3Packages;
+in pkgs.mkShell rec {
+  name = "impurePythonEnv";
+  venvDir = "/tmp/cmake-init_venv";
+  buildInputs = [
+    # A Python interpreter including the 'venv' module is required to bootstrap
+    # the environment.
+    pythonPackages.python
+
+    # This executes some shell code to initialize a venv in $venvDir before
+    # dropping into the shell
+    pythonPackages.venvShellHook
+
+    # Those are dependencies that we would like to use from nixpkgs, which will
+    # add them to PYTHONPATH and thus make them accessible from within the venv.
+    #pythonPackages.numpy
+    #pythonPackages.requests
+    pkgs.wget
+
+    # In this particular example, in order to compile any binary extensions they may
+    # require, the Python modules listed in the hypothetical requirements.txt need
+    # the following packages to be installed locally:
+    #
+  ];
+
+  # Run this command, only after creating the virtual environment
+    #pip install -r requirements.txt
+  postVenvCreation = ''
+    unset SOURCE_DATE_EPOCH
+    pip install cmake-init
+  '';
+
+  # Now we can execute any commands within the virtual environment.
+  # This is optional and can be left out to run pip manually.
+  postShellHook = ''
+    unset SOURCE_DATE_EPOCH
+  '';
+
+}