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;
+  };
+}

pkgs/top-level/python-packages.nix

@@ -265,31 +265,8 @@ in {
   aafigure = callPackage ../development/python-modules/aafigure { };
 
   altair = callPackage ../development/python-modules/altair { };
-  vega = buildPythonPackage rec {
-    name = "vega-0.4.4";
 
-    src = pkgs.fetchurl {
+  vega = callPackage ../development/python-modules/vega { };
-      url = "mirror://pypi/v/vega/${name}.tar.gz";
-      sha256 = "08k92afnk0bivm07h1l5nh26xl2rfp7qn03aq17q1hr3fs5r6cdm";
-    };
-
-    buildInputs = [ self.pytest ];
-    propagatedBuildInputs = with self; [ jupyter_core pandas ];
-
-    meta = {
-      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;
-      platforms = platforms.linux;
-      maintainers = with maintainers; [ teh ];
-    };
-  };
 
   acme = buildPythonPackage rec {
     inherit (pkgs.certbot) src version;