3.1.3 downloadPkgs, doPackageLists, and package.basepath

I encountered some trouble upgrading from 3.0.3 ...

In the old version I could invoke yum from within another python
program in a manner like

> pkg_data = yum_session.doPackageLists('available')
> wanted_list = filter_packages(pkg_data.available)
> yum_session.downloadPkgs(wanted_list)

But this no longer works -- the problem seems to be that package
objects returned from doPackageLists no longer have the basepath field
set, which seems to be necessary for downloadPkgs to actually get
them...

Advice on what to do differently would be appreciated.  Thanks,

Tammo