ModuleNotFoundError: No module named 'skbuild'

[pfaion]

Collecting git+https://github.com/pupil-labs/apriltags
  Cloning https://github.com/pupil-labs/apriltags to /tmp/pip-rw9h_3fg-build
    Complete output from command python setup.py egg_info:
    Traceback (most recent call last):
      File "<string>", line 1, in <module>
      File "/tmp/pip-rw9h_3fg-build/setup.py", line 11, in <module>
        from skbuild import setup
    ModuleNotFoundError: No module named 'skbuild'

Installation via pip fails for older versions pip that do not parse the build dependencies correctly.
We should check the pip version in setup.py and throw an error with a message on how to update pip for older versions of pip!

[pfaion]

Note: I had pip version 9.0.1 on Ubuntu 18.04 (system python 3.6.8) when experiencing this issue.

[pfaion]

See e.g. this PR to Pupil: pupil-labs/pupil#1775
where a user apparently ran into this problem when installing the dependencies for Pupil.

A good solution could be to just add pip > X as install_requires. Would that work? Need to find the minimal pip version that supports PEP517 and PEP518,

[pfaion]

Adding pip to install_requires won't work, as setup.py will be parsed (and skbuild tried to import) before the requirements will be installed.

A quick google did not result in any genius way of how to foolproof a pure PEP517/518 package to be installed from old pip versions. I guess we can only add this to the README here.