Error with Cython and numpy dependency

[mchalela]

Hello! I'm trying to install pmesh via pip install pmesh but I keep getting an error with cython.
It seems that you first need to have cython installed to be able to run line 46 of the setup, and also numpy to run line 3.
Is there a way to avoid using cython and numpy in the setup stage? I'm developing a package that will probably use pmesh as a dependency so numpy and cython won't be previously installed.
Thank you!!

pmesh/setup.py

Line 3 in 5c3a226

import numpy

pmesh/setup.py

Lines 46 to 59 in 5c3a226

	from Cython.Build import cythonize
	extensions = cythonize(extensions)
	setup(
	name="pmesh", version=find_version("pmesh/version.py"),
	author="Yu Feng",
	description="Particle Mesh in Python",
	package_dir = {'pmesh': 'pmesh'},
	packages= ['pmesh', 'pmesh.tests'],
	install_requires=['cython', 'numpy', 'mpi4py', 'mpsort', 'pfft-python'],
	license='GPL3',
	ext_modules = extensions,
	extras_require={'full':['abopt'], 'abopt':['abopt']}
	)

[mortele]

@mchalela You can add a pyproject.toml file with [build-system] requires specifying dependencies which need to be present before setup.py is run, cf. PEP 518. Using this you can ensure numpy and cython is installed before any other dependencies, thus fixing the problem. Note that this only handles the install dependencies when using pip, running python3 setup.py install will still fail.

Alternatively, open a pull request doing exactly this in pmesh and fix the problem further upstream, so to say.

[rainwoodman]

A PR with a toml file is highly welcome. It sounds like we do need to tag a new release on pypi to make the file effective?