Hi, pip 21 is (likely) going to drop the fallback of running `setup.py install` if wheels can not be build. I've been using that fallback b/c wheels are not installed immediately on completion and do not respect the dependency order for build-time, whereas `setup.py install` does. With a "pyproject.toml" file, which pip supports, I can control the build environment again and that works quite nicely for CPython. For PyPy, however, I am unable to make selections based on the PyPy version. I can make selections based on the PyPy Python version, e.g. 2.7, 3.5, etc., but I'm talking about the actual PyPy version (e.g. 7.2.0). Does anyone know how to add a marker based on the PyPy version in a pyproject.toml file? Or, how else to enforce build dependencies for pip in the same way that can be done with the pyproject.toml file? Thanks, Wim -- WLavrijsen@lbl.gov -- +1 (510) 486 6411 -- www.lavrijsen.net