python.pkgs.lxml: move expression

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

···
+{ stdenv
+, buildPythonPackage
+, fetchPypi
+, libxml2
+, libxslt
+}:
+
+buildPythonPackage rec {
+  pname = "lxml";
+  version = "3.8.0";
+
+  src = fetchPypi {
+    inherit pname version;
+    sha256 = "15nvf6n285n282682qyw3wihsncb0x5amdhyi4b83bfa2nz74vvk";
+  };
+
+  buildInputs = [ libxml2 libxslt ];
+
+  hardeningDisable = stdenv.lib.optional stdenv.isDarwin "format";
+
+  meta = {
+    description = "Pythonic binding for the libxml2 and libxslt libraries";
+    homepage = http://lxml.de;
+    license = stdenv.lib.licenses.bsd3;
+    maintainers = with stdenv.lib.maintainers; [ sjourdois ];
+  };
+}

pkgs/top-level/python-packages.nix

···
 
   logilab-constraint = callPackage ../development/python-modules/logilab/constraint.nix {};
 
-  lxml = buildPythonPackage ( rec {
-    name = "lxml-3.8.0";
-
-    src = pkgs.fetchurl {
-      url = "mirror://pypi/l/lxml/${name}.tar.gz";
-      sha256 = "15nvf6n285n282682qyw3wihsncb0x5amdhyi4b83bfa2nz74vvk";
-    };
-
-    buildInputs = with self; [ pkgs.libxml2 pkgs.libxslt ];
-
-    hardeningDisable = stdenv.lib.optional stdenv.isDarwin "format";
-
-    meta = {
-      description = "Pythonic binding for the libxml2 and libxslt libraries";
-      homepage = http://lxml.de;
-      license = licenses.bsd3;
-      maintainers = with maintainers; [ sjourdois ];
-    };
-  });
+  lxml = callPackage ../development/python-modules/lxml {inherit (pkgs) libxml2 libxslt;};
 
   lxc = buildPythonPackage (rec {
     name = "python-lxc-unstable-2016-08-25";