Stupid question: "import matplotlib" is failing despite matplotlib being installed on my system (OS X) and working fine when I run python from the command line.

Stupid question: "import matplotlib" is failing despite matplotlib being installed on my system (OS X) and working fine when I run python from the command line. I'm guessing it's something to do with my PYTHONPATH not getting imported properly. Does anyone have any idea how to fix this? Edited to add: this is the first time I've properly tried LightTable and oh my god what a gorgeous piece of software. It's glorious. Just.. yeah. Job well done! :)