The question you linked to explains it very well. There is no such thing as "PyQt Designer". There is only Qt Designer, which should be installed along with Qt itself.

PyQt提供了一个插件，该插件可以启用自定义窗口小部件来用python 为Qt Designer编写.除非安装了PyQt，否则默认情况下会安装此插件，除非使用--no-designer-plugin选项明确将其配置为不安装.

PyQt provides a plugin that enables custom widgets to be written in python for Qt Designer. This plugin is installed by default when PyQt is installed, unless it was explicitly configured not to by using the --no-designer-plugin option.

如果启动Qt Designer并打开帮助"->关于插件"，您应该会在其中看到某种python或pyqt插件-在Mac OSX上，我认为该插件应安装在/Developer/Applications/Qt/plugins/designer/中.)

If you start Qt Designer and open Help -> About Plugins, you should see some kind of python or pyqt plugin listed there - on Mac OSX, I think the plugin should be installed in /Developer/Applications/Qt/plugins/designer/).