python.pkgs.vega: move to separate expression

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

@@ -0,0 +1,30 @@
+{ stdenv, buildPythonPackage , fetchPypi
+, pytest, jupyter_core, pandas }:
+
+buildPythonPackage rec {
+  pname = "vega";
+  version = "0.4.4";
+  name = "${pname}-${version}";
+
+  src = fetchPypi {
+    inherit pname version;
+    sha256 = "08k92afnk0bivm07h1l5nh26xl2rfp7qn03aq17q1hr3fs5r6cdm";
+  };
+
+  buildInputs = [ pytest ];
+  propagatedBuildInputs = [ jupyter_core pandas ];
+
+  meta = with stdenv.lib; {
+    description = "An IPython/Jupyter widget for Vega and Vega-Lite";
+    longDescription = ''
+      To use this you have to enter a nix-shell with vega. Then run:
+
+      jupyter nbextension install --user --py vega
+      jupyter nbextension enable --user vega
+    '';
+    homepage = https://github.com/vega/ipyvega;
+    license = licenses.bsd3;
+    maintainers = with maintainers; [ teh ];
+    platforms = platforms.linux;
+  };
+}