Kivy requires Cython to be installed by the user in some situations, which makes depending on it as a package problematic

[flaviusb]

Versions

• Python: Python 3.6.5
• OS: Linux (4.12.12-gentoo x86_64)
• Kivy: 1.10.1
• Kivy installation method: install_requires in setup.py

Description

I am trying to create a package that uses kivy, that a user can install using pip, so that I can upload it to PyPI. This is a package that a user should be able to have as a dependency in their own package using the usual 'install_requires' method in setup.py, ideally using vanilla setuptools. At present, I have to install Cython separately in order to get Kivy to install, as Kivy does not correctly manage its dependencies.

Code and Logs

After clearing out wheel cache, to replicate installing on a fresh system, and in the directory I am developing the package in:

$ virtualenv --no-site-packages install
Using base prefix '/usr'
New python executable in /home/flaviusb/code/rvit/install/bin/python3.6
Also creating executable in /home/flaviusb/code/rvit/install/bin/python
Installing setuptools, pip, wheel...done.
$ . install/bin/activate
(install) $ pip install -e .
Obtaining file:///home/flaviusb/code/rvit
Collecting kivy (from rvit==0.1)
  Using cached https://files.pythonhosted.org/packages/7d/8b/89d220b7f96dc2662b81319067f679b4cd73cda66f4aa850db5b6c6cfc7a/Kivy-1.10.1.tar.gz
    Complete output from command python setup.py egg_info:
    Using distutils
    
    Cython is missing, it's required for compiling kivy !
    
    
    Traceback (most recent call last):
      File "<string>", line 1, in <module>
      File "/tmp/pip-install-qf1pe7c9/kivy/setup.py", line 232, in <module>
        from Cython.Distutils import build_ext
    ModuleNotFoundError: No module named 'Cython'
    
    ----------------------------------------
Command "python setup.py egg_info" failed with error code 1 in /tmp/pip-install-qf1pe7c9/kivy/

[tshirtman]

Yes, i opened this one #5558 some time ago to try to find a solution to this, i tried to ship the code in the package to avoid the build time dependency on cython, but since the generated C code depends on the python version, we would need multiple source packages, and i didn't investigate yet if this was possible.

[tito]

IMO, either there is a wheel so you don't need Cython, either you install source version therefore Cython is required? Trying to create a source version containing all potential python version seems counter-intuitive

[tshirtman]

Some platforms don't have a wheel (e.g rpi though it seems it would be possible https://www.piwheels.org/), and the linux wheel certainly can't be official yet (as it depends on the provisionnal manylinux2010 definition pypa/manylinux#182).

[flaviusb]

@tito for clarity, just confirming that in the case there is no wheel, the user would have to separately install cython first, as putting it in the install_requires of a project that depends on kivy would not work, as pip builds each dependency for a project isolated so that it can only see it's own dependencies plus the user environment, and kivy does not register a dependency on cython through install_requires or other equivalent means in these problematic situations at present.

[flaviusb]

Would a work around like having an extras option to override the cython checking segment of kivy's setup.py to add cython to the install_requires be something that makes sense for kivy (eg https://setuptools.readthedocs.io/en/latest/setuptools.html#declaring-extras-optional-features-with-their-own-dependencies)?

Edit: spelling

[flaviusb]

Some related issues I had not found until now:
#5375 #4675 pfassina/callllama#2

[vkuehn]

for Cpython and Pygame I have been fallen in the same trapp. Manually installing worked.
However it's a pain when you like to create a setup

[rootVIII]

Having this issue on Ubuntu 16.04 with python3... bummer

[vkuehn]

from the comments before I would expect that this is always an issue

[farleylai]

Since the release cycle is kind of long, installing from the repo is a common practice. Without Cython declared as the dependency, pip is not going to install from git in the right order of a requirements.txt.

[ghost]

pip installs setup_requires, doesn't it? (because it runs setup.py and that one will then do that first thing before calling any of the build_ext things, so if Cython is only imported in-line inside the build_ext code instead of globally at the top of the setup.py file it should still work) Would it therefore help to add Cython to setup_requires instead of install_requires or requirements.txt? I imagine that way it might not end up packaged in the actual binary wheel later on

[flaviusb]

@Jonast The PR here #5998 deals with this issue; the comments and commits there document how this actually ends up working out.

[flaviusb]

The PR #5998 has been merged, which should fix this issue.