You can try to do:
> import gc gc.collect()
> This will force the garbage collector to kick in, which
> sometimes may help.
I'm not seeing any leak on linux with my standard memory leak test, eg
unit/memleak_hawaii3.py
in CVS.
Have you read over
http://matplotlib.sourceforge.net/faq.html#LEAKS
Unfortunately, the standard idiom I use for testing memory usage is
platform specific.
A complete script which exposes the leak would help...
JDH