I recently wanted to mess around with Vpython and followed the instructions on this site: http://vpython.org/contents/download_mac.html
Before this point, I had python up and running on my laptop and installed libraries using macports. Since following the installation steps described on the Vpython page, I can no longer use any of my scipy related libraries. For example, when importing numpy it just says
ImportError: No module named pylab
Also, when looking in /Library/Python/2.7/site-packages/ scipy isn't present, even though macports says py27-scipy is installed (and I've tried reinstalling).
I'm guessing the python install (which I naively thought was standalone) that I preformed when installing Vpython has messed up a path or something and I'm not quite sure how to fix it.
Most likely your shell PATH has been modified so that another Python is being found before the MacPorts one, the one that has Pylab installed to it. Try typing /opt/local/bin/python2.7, assuming you've used the default MacPorts install prefix.
MacPorts Pythons do not install into /Library/Python or /Library/Frameworks.