gistfile1.txt

      "fixtures" = python.overrideDerivation super."fixtures" (old: rec {
        # nativeBuildInputs = old.nativeBuildInputs ++ [ pkgs.pythonPackages.testtools ];                                                                                                                          
        # patchPhase = ''                                                                                                                                                                                          
        #   sed -i -e 's/, "testtools (>=0.9.22)"//'                                                                                                                                                               
        # '';                                                                                                                                                                                                      
      });

      "testtools" = python.overrideDerivation super."testtools" (old: rec {
        propagatedNativeBuildInputs = remove "fixtures" old.propagatedNativeBuildInputs;
        # nativeBuildInputs = old.nativeBuildInputs ++ [ self."fixtures" ];                                                                                                                                        
      });