Right now the best impl info is not exported for python_prepare_all(). I don't recall why it is like this. It may had something to do with not having build dir at the point and therefore being unable to use the common function. But I don't see anything wrong with having the impl setup immediately. Anyone can think of any potential issues?
Yeah, I think it certainly makes sense to set PYTHON and EPYTHON. Not sure about BUILD_DIR though.
That was done a long time ago.