How would you select/turn on optional packages?

On Thu, Jan 17, 2019 at 12:22 PM PIERRE AUGIER <> wrote:

I can't use pyproject.toml for some projects with "optional build dependencies" because of build isolation.

However, it would be very useful because we have also real build dependencies.

I created an issue in pip repository ( but it seems to be a more general problem.

I didn't find anything about such potential problem in PEP 517/518. Any thoughts how it can be solved?

In the issue, I propose this:

# Minimum requirements for the build system to execute.
requires = [
    "setuptools", "wheel", "numpy", "cython", "jinja2", "fluidpythran>=0.1.7"
# packages that are used during the build only if they are installed:
optional = ["mpi4py", "pythran"]


Pierre Augier
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