There is a Valgrind suppression file distributed with Python that gets rid of most of the false positives, but does not give particularly good diagnostics for memory allocated through pymalloc. To properly analyse leaks, you often need to recompile Python with pymalloc.
As I don’t like having to recompile Python I took a look at Valgrind’s client API, which provides a way for a program to detect whether it is running under Valgrind. Using the client API I was able to put together a patch that automatically disables pymalloc when appropriate. It can be found attached to bug 2422 in the Python bug tracker.
The patch still needs a bit of work before it will be mergeable with Python 2.6/3.0 (mainly autoconf foo). I also need to do a bit more benchmarking on the patch. If the overhead of turning on this patch is negligible, then it’d be pretty cool to have it enabled by default when Valgrind is available.