Detect Python Defaults [opinions wanted]

Languages Python
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Hey Folks,

If we were to detect python defaults, like we do with other languages, for example running make if a Makefile is present, or possibly running pytest if *_test.py is present, what should we be detecting? What should we look out for?

Cheers

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  1. pyproject.toml (see PEP 517 / PEP 518)
  2. tox.ini
  3. setup.py/setup.cfg
  4. requirements.txt

If pytest is detected in requirements, just run pytest without args (they are probably specified in pytest.ini, setup.cfg or pyproject.toml already).
Oh, and upgrade pip to the latest version so that it could pick up pyproject.toml magic. Upgrade setuptools so that it could pick up pure setup.cfg.

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With regards to tox, the presence of tox.ini is a good indicator that tox is what is wanted, however that only always holds true if there is a single travis python job, or if envvar TOXENV is set. If there are multiple python jobs, it is quite likely that the tox.ini is intended for developers to run locally in order to test multiple python versions, and isnt suitable for travis to be invoking in each job, and running tox in Travis will often fail in that scenario.

However, travis could install tox-travis [COI: I am one of the maintainers] to make tox choose the correct testenv to correspond with the Travis python version in each job. If Travis doesn’t want to depend on tox-travis, the alternative is to set TOXENV (if not already set) to py27, py36 (etc), pypy, pypy3, etc. It is a fairly simple string transform from TRAVIS_PYTHON_VERSION to TOXENV for the most common cases.

Fairly common now, but worth noting that the latest tox version does not support py2.6, py3.0-3.3 and may also fail on 3.8-dev (at least in py37 early dev cycle it didnt handle this, but maybe that has been fixed), and tox-travis also doesn’t support those versions either. You would need to go back a long way in the tox version history to find a version which worked with py3.3 or py2.6, and may not even find a version which supported py3.0-2 . pytest is roughly the same in this regard. tox-travis did have some special voodoo to keep py3.2 and 3.3 supported after virtualenv and tox killed them, but that was discarded in tox-travis v0.11.

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Another type of Python project worth supporting is Django projects / apps.

The presence of manage.py is one clear indicator . They should be tested with python manage.py test
c.f. https://docs.djangoproject.com/en/2.2/topics/testing/overview/#running-tests

Sometimes the project chooses to not check in manage.py , in which case django-admin test can also be used, but that is a bit error prone as the Django settings.py for testing is often different from the settings.py used for production, and the testing one is often in a non-default subdirectory somewhere to avoid it being used in production. pytest-django can usually help with that.