Matplotlib 0.80-r1 does not install 'pytz' module, but depends on it (dates.py attempts to import timezone class from pytz, but fails). From the other side, dev-python/pytz requires matplotlib version higher 0.82 and can not be installed separately. dev-lang/python-2.4.2 dev-python/matplotlib-0.80-r1 portage tree: 2006-07-13
Please, read the changelog. The stuff collides. You need a higher version if you want both installed.
Ok, thanks. I have unmasked latest ebuild and successfully emerged it (with python-dateutil and pytz). Now matplotlib imports all required modules just fine.