On May 30, 2017, at 12:29 PM, Thomas Kluyver <thomas@kluyver.me.uk> wrote: What about saying that the copying step, if necessary, is part of the build backend's responsibilities? I.e. pip doesn't copy the whole directory to a temporary build location, but the build backend may decide to do that at its discretion when it's asked to build a wheel. pip would continue to handle this for setup.py builds.