Try ZODB/ZEO, you will be able to access native python data structures (possibly cached in memory) from multiple python processes.
ZEO and ZODB are nice, but using them also does not solve the problem - there is still one serialization for every update and one de-serialization for every independent client/dirty-read. I love Zope and Plone and use them for a lot of situations (I won't think twice when someone wants a CMS for their intranet), but I sure would like to be able to set "zserver-threads" to 64, buy a Sun Niagara-based server and just live happy with it watching how all thread units get their fair share of usage.