Adjust setup.py to reflect PEP-518, instead of throwing a "you need cython" error.

[Demetrio92]

Description

Fix setup.py to install cython, instead of giving the user an error.

pypa/pip#5761 (comment)
https://www.python.org/dev/peps/pep-0518/

Code to reproduce

On a fresh vitrual enviroment:

pip install cartopy

Traceback

(mypython) me@my_laptop:~/path/tmp$ python
Python 3.5.3+ (default, Nov 29 2017, 08:55:08) 
[GCC 5.4.0 20160609] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> 
(mypython) me@my_laptop:~/path/tmp$ pip install cartopy
Collecting cartopy
  Using cached https://files.pythonhosted.org/packages/f5/7a/4a16db7c81f11b3c5889c5b913d9a5724c704a6947c5a87ec59c4a8985ac/Cartopy-0.16.0.tar.gz
    Complete output from command python setup.py egg_info:
    Traceback (most recent call last):
      File "/tmp/pip-install-7r1fl7u1/cartopy/setup.py", line 47, in <module>
        from Cython.Distutils import build_ext
    ImportError: No module named 'Cython'
    
    During handling of the above exception, another exception occurred:
    
    Traceback (most recent call last):
      File "<string>", line 1, in <module>
      File "/tmp/pip-install-7r1fl7u1/cartopy/setup.py", line 49, in <module>
        raise ImportError('Cython 0.15.1+ is required to install cartopy.')
    ImportError: Cython 0.15.1+ is required to install cartopy.
    
    ----------------------------------------
Command "python setup.py egg_info" failed with error code 1 in /tmp/pip-install-7r1fl7u1/cartopy/

Operating system

Ubuntu 16.04

[benoit-pierre]

Technically, that's not adding PEP 518 support, just fixing the existing workaround so it works with setuptools>=36.7.0.

For PEP 518 support, a new pyproject.toml file should be added:

[build-system]
requires = ["Cython>=0.15.1", "numpy>=1.10", "setuptools", "wheel"]

[felixdivo]

Great that this is finally solved! 😄

[chaitan94]

It's great that this is finally solved.

But unfortunately it has also been un-solved later 😛
Refer to: 454a911

From the commit it seems this was because it results in some version mismatch in numpy coming from build dependencies vs numpy comping from actual dependency (although I am not completely sure what the exact reason is).

I am not sure how cartopy's build works, and what solutions are there to prevent this, but can this possibly be solved with a slightly modern build tool like poetry/dephell? I know that is sort of significant change to the project, but if that sounds like a good idea maybe I can try and take a dig at this. Would love to know maintainers thoughts on this (maybe from @dopplershift, @pelson or @QuLogic probably?).

[chaitan94]

Should this issue be ideally re-opened at least?