Transitioning to Python 3

[emiliom]

This is a stub issue, for now. We have issues and materials on the Python 3 transition scattered throughout other repos. Let's try to integrate generic elements (ie, information not specific to the ODM2 package at hand) here, on this issue and/or on a markdown document in this repo.

Some places where we've discussed this:

• Python 3 WOFpy#231
• python 3.x compatibility  ODM2PythonAPI#58

[aufdenkampe]

@emiliom, thanks for posting this new cross-org issue for collecting the various efforts to transition to Python 3! This is a great place for that.

[aufdenkampe]

I just talked to @miguelcleon who mentioned he just tried installing the ODM2PythonAPI on Python 3 and it didn't work, and that he was looking into it right now because he had thought it would based on this work:

• python 3.x compatibility, python 3.x compatibility  ODM2PythonAPI#58
• Python 3 compatibility and flake8, Python 3 compatibility and flake8 ODM2PythonAPI#111

However, as @emiliom mentioned in ODM2/ODM2PythonAPI#157 (comment), he didn't "recall anyone doing significant and sustained testing for Python 3 compatibility."

It seems that now might be the right time to push for this testing and development of a Python 3 compatible ODM2PythonAPI.

In addition to @miguelcleon's current interest, others are also working on this or have an immediate need, including:

• @steveskrip, @tslawecki and I are planning on setting up a Python 3 environment for ODM2 to support some machine learning applications.
• @roelofversteeg and his team, @erekalper & @dougvj, have developed a Python 3 compatible variant of the ODM2PythonAPI to work with a proposed, draft ODM2.1 (https://github.com/ODM2/ODM2/milestone/1).

Can some of the suggestions I had made in ODM2/WOFpy#230 (comment) or ODM2/WOFpy#230 (comment) help?

• A key point from https://docs.python.org/2/howto/pyporting.html is that "modernizing your Python 2 code to also support Python 3 is largely automated for you."
• Does a compatibility layer like this help: https://python-future.org?

[miguelcleon]

@aufdenkampe Ok, the problem maybe specific to the environment I was trying to install too. I received the error below. I was trying to install it in the same environment as ODM2 Admin.

UnsatisfiableError: The following specifications were found to be in conflict:
  - odm2api
  - social-auth-core
Use "conda info <package>" to see the dependencies for each package.

I copied the conda environment and removed social-auth-core, which is required by social-auth-app-django so that was removed as well. Then I got:

UnsatisfiableError: The following specifications were found to be in conflict:
  - defaults/linux-64::numpy==1.15.4=py36h1d66e8a_0
  - odm2api
Use "conda info <package>" to see the dependencies for each package.

So it looks like it is not is not working with the version of numpy in my environment either.

I then tried installing on a fresh Python 3.6 conda environment but that required a downgrade to python 2.7. So I guess this is an issue with conda and how the odm2pythonapi is setup. It may well work if you just install using pip directly into python without conda but I'm trying to do everything in conda environments.

[emiliom]

Regarding the ability to install odm2api on Py3, w/o overly restrictive dependency version pinning: I'm not seeing any dependency version pinning in its requirements files and conda recipe. So it probably should be built ok via pip install on Py3, with some flexibility for specific dependency version requirements from other packages.

@miguelcleon There is no Py3 odm2api conda package available at this time! So, the conda package that's there only works with 2.7, by design. See https://anaconda.org/conda-forge/odm2api/files

Still, the ability to pip install it on Py3 doesn't mean it actually works Ok on Py3! There's no guarantee, and it's unclear how much work one would have to invest to deem it Py3-compatible, including both testing and tweaking the code.

It seems that now might be the right time to push for this testing and development of a Python 3 compatible ODM2PythonAPI.

Well, it's only the right time if there are people willing and able to put in the work! That's both the base work, plus the work to review PRs. Speaking for myself, I don't think I can make a commitment of that sort this month.

[emiliom]

I guess I should add that this discussion should be happening over at https://github.com/ODM2/ODM2PythonAPI/, not here. This issue is for general resources and topics involving the transition to Python 3, not discussions for any one package in particular.

[emiliom]

• https://docs.python.org/2/library/2to3.html. 2to3 is installed in Python by default. eg, in a conda env, its in env/myenv/bin
• Modernize: https://python-modernize.readthedocs.io/en/latest/
• Futurize: http://python-future.org/automatic_conversion.html
• http://python-future.org has a lot of very helpful documentation and resources about the Py3 transition
• Sunsetting Python 2 (python.org)