Rails has some weaknesses, but your post is missing them, Ian. Several people have had the reaction "but what if you want to do more than simple scaffolding?" but it totally misses the point. Scaffolding is just a development aid to get things online quickly. You'd never use it as a finished product. Doing joins and more complex screens is still easy.
The integration within Rails goes very deep, yet it retains flexibility. That's something that can't be achieved by sticking pieces together, as Phillip noted. If you want a Rails-like framework in Python, I suggest you get your hands dirty and start from scratch.