Can I just say that it annoys the living fuck out of me that, after having basically made the mental switch to Python 3, it turns out that a lot of the powerful non-commercial packages for doing math and science haven't been ported/translated and are only compatible up to Python 2.x!!!
Specifically, dealing with mathematical graphics: the standard sharp object appears to be matplotlib; the examples show some very nice graphics, but it won't talk to Python 3. It's been like two years, people! I understand that some projects aren't actively maintained, but if you do, and there's a new version of the scripting language out, don't ignore that fact!
Bah. Anyway, the main point of this post is to record for myself and my alteri nos that IDLE doesn't deal with matplotlib/pylab in interactive mode. So don't try, just use the basic shell (or, apparently, switch IDEs to something called ipython) if you need interactive. Which kinda sucks, since the whole reason I'm going down this particular yellow brick road is to try to program a very basic visualization tool for finite posets, something similar in feel to the congruence lattice/subalgebra lattice tool in Ralph Freese's universal algebra calculator.