I just upgraded to Mountain Lion and here are some of my notes related to scientific Python installs.

If you’ve already got a working installation it will likely continue to work after upgrading. Regardless of whether you plan to keep using an existing install or make a new one you’ll probably want to do the following two things:

Xcode

You’ll need a Mountain Lion compatible set of command line tools and development libraries so reinstall Xcode or the Command Line Tools for Xcode. I personally prefer the later now that I use Sublime Text 2 for code editing. If you install Xcode make sure to install the command line tools from the preferences.

X11

ML doesn’t come with X11 installed so install XQuartz from http://xquartz.macosforge.org/ if you anticipate needing X11.

Python Libraries

• NumPy compiles without issue.
• SciPy is waiting on a small change before it will compile on Mountain Lion. I expect that to go in soon and they may release SciPy 0.10.2 to make it Mountain Lion compatible. Even if they don’t you’ll be able to install from the GitHub repository once the change is made.
• matplotlib must be installed from the GitHub repository at this time.