pythonPackages.ruamel_yaml: fix build

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

@@ -1,9 +1,11 @@
-{ stdenv
+{ lib
 , buildPythonPackage
 , fetchPypi
 , ruamel_base
 , ruamel_ordereddict
+, ruamel_yaml_clib
 , isPy3k
+, isPyPy
 }:
 
 buildPythonPackage rec {
@@ -15,13 +17,21 @@ buildPythonPackage rec {
     sha256 = "412a6f5cfdc0525dee6a27c08f5415c7fd832a7afcb7a0ed7319628aed23d408";
   };
 
-  # Tests cannot load the module to test
+  # Tests use relative paths
   doCheck = false;
 
   propagatedBuildInputs = [ ruamel_base ]
-    ++ stdenv.lib.optional (!isPy3k) ruamel_ordereddict;
+    ++ lib.optional (!isPy3k) ruamel_ordereddict
+    ++ lib.optional (!isPyPy) ruamel_yaml_clib;
 
-  meta = with stdenv.lib; {
+  # causes namespace clash on py27
+  dontUsePythonImportsCheck = !isPy3k;
+  pythonImportsCheck = [
+    "ruamel.yaml"
+    "ruamel.base"
+  ];
+
+  meta = with lib; {
     description = "YAML parser/emitter that supports roundtrip preservation of comments, seq/map flow style, and map key order";
     homepage = https://bitbucket.org/ruamel/yaml;
     license = licenses.mit;