[Distutils] setup_requires for dev environments

[Steve Dower]

Donald Stufft wrote:
> So yea, what's the actual problem that this is attempting to solve?

ISTM (whether this is the actual intent or not) that this would be handy to differentiate between the dependencies needed when installing from a wheel vs. an sdist. Daniel's example of setup_requires including cython suggests to me that a wheel would include the compiled output and cython is not required in that case.

I don't personally have a use case for this right now, though it does seem like it has potential to refer to a Python package that acts as a front-end for a compiler (and perhaps downloader/installer... hmm...)

Cheers,
Steve