As much as I despise the nodejs dependency hell, PhantomJS is a better solution when compared to wkhtml, so a Python-PhantomJS wrapper would be a significantly better product imho.
PhantomJS has stand-alone binaries that you can just call from Python if you wanted.
That's all this project does.
At least for screenshots, the headless support recently introduced into chrome might be the most straightforward solution, with the fewest pieces.