because I just wasted nearly an hour working it out from first principles

In Python >= 2.5, if you need to do

    from . import module

but you don't know the name of module until runtime, this is how you do it:

    mod = getattr(__import__('', globals(), locals(),
                             [name], 1), name)

(This is going on my big list of things I will change when I am the BDFL.)