Reduce duplication of dependency information

[IRDonch]

Summary

Currently, all runtime dependencies are listed in both requirements.txt and setup.py, except that they sometimes have differing version constraints. This is confusing and increases the amount of work a maintainer needs to do when updating the dependency list.

Fix it by moving all runtime dependencies to a separate file (requirements-core.txt) and referencing that file from both setup.py and requirements.txt. Combine all version constraints from both original files.

Unfortunately, some things still need to be duplicated:

• The OpenCV dependency varies depending on environment variables, and that logic can't be replicated with a requirements file. So OpenCV has to be listed separately in setup.py and requirements.txt.

• Cython is a build dependency, not a runtime dependency, so it shouldn't go into requirements-core.txt. It would technically be possible to move it to a separate requirements file and reference from there, but it's just one dependency, so it doesn't seem worth it.

How to test

Try to run pip install -r requirements.txt. (The installation through pip install . is covered by CI.)

Checklist

• I submit my changes into the develop branch
• I have added description of my changes into CHANGELOG
• [ ] I have updated the documentation accordingly No update should be needed
• [ ] I have added tests to cover my changes
• [ ] I have linked related issues

License

• I submit my code changes under the same MIT License that covers the project.
  Feel free to contact the maintainers if that's a concern.
• I have updated the license header for each file (see an example below)

# Copyright (C) 2021 Intel Corporation
#
# SPDX-License-Identifier: MIT

[zhiltsov-max]

Technically, in requirements.txt we could just use --no-binary, and I'd prefer this solution. But it is not supported in setup.py.

[zhiltsov-max]

What do you think about adding a couple of extra requirement files?
-testing with pytest
-ci with coverage
-plugins with TF, TF-gpu, pandas?

[zhiltsov-max]

Also, you asked about fixed dependency versions in setup.py - consult this doc https://packaging.python.org/discussions/install-requires-vs-requirements/.

[IRDonch]

What do you think about adding a couple of extra requirement files?
-testing with pytest
-ci with coverage
-plugins with TF, TF-gpu, pandas?

I think the most sensible scheme would be as follows:

• requirements-core.txt - core runtime dependencies (the file I created in this PR)
• For each plugin that has additional dependencies, requirements-<plugin>.txt. The setup.py equivalent would be an entry in extras-require.
• requirements-dev.txt - development dependencies (pytest, pylint, etc.). I don't think we need to split this into test, coverage or whatever.
• requirements.txt - master file that includes all of the above.

That said, the above scheme only makes sense if we want to keep runtime dependencies in requirements.txt files, which I'm not sure about. A simpler scheme would be to keep them only in setup.py and have only a requirements-dev.txt and a master requirements.txt file that just contains:

-e .[plugin1,plugin2]
-r requirements-dev.txt

[IRDonch]

Also, you asked about fixed dependency versions in setup.py

I... don't think I did, though? :-) I don't think setup.py should have fixed dependency versions, and the document you linked agrees with me.

[IRDonch]

So, what now? Should I change anything?

[zhiltsov-max]

Do you want to add anything into CONTRIBUTING.md?

[IRDonch]

Do you want to add anything into CONTRIBUTING.md?

Not really. I don't think anything I did here conflicts with anything that CONTRIBUTING.md says.