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Software Must Support Recent Version(s) of Python

This is one of the tier 2 standards. See full list on the main page.

Short description

We require that all Python software 'support' one or more 'recent' versions of Python. Currently, we consider 'recent' versions to include 3.6, 3.7, and 3.8. We define 'support' in this context such that:

  • The Python software is fully operational with no errors when invoked from an interpreter that uses the recent Python version(s)
  • Any future contributions to the software must also adhere to the above requirement
  • Any provided software environment file(s) in the repository (i.e. environment.yml, requirements.txt, setup.py), must all be consistent in their listings of supported Python version(s)
  • Any defined software environments within continuous integration builds (i.e. Jenkins or Travis) must also be using the supported Python version(s)

Importance of this standard

With Python being free and open-source, the Python community continues to build and improve the existing language, resulting in periodic releases of new versions of the Python native library as well as many third-party libraries that we commonly use at STScI (e.g. bokeh, astropy, numpy, etc.). As such, over time the Python software that we write becomes outdated, and the versions of the dependencies that we rely on become unsupported. This in turn makes it difficult for future developers to maintain existing software and their environments, as well as build new features. Furthermore, users of INS JWST software may opt to install the software in environments that use the latest version of Python, and they may get deterred if they have to downgrade their environment or existing dependent software. For these reasons, we make an effort to keep our software operational with newer Python versions, as does the Python community as a whole, in order to avoid some of these future issues. As such, we are requiring teams to support at least one recent version of Python. Teams may also choose to support several of the most recent versions.

How to apply this standard

For software that must be upgraded from Python 2.x to Python 3.x, the tool 2to3 can be used to show (and optionally apply) all of the necessary changes. For a general description of what aspects of the Python 2.x code must be changed in order to comply with Python 3.x, see the official Python documentation on 'updating your code'.

For software that must be upgraded from Python <=3.5 to Python >=3.6, unfortunately an automated tool akin to 2to3 does not exist for showing what could be upgraded in your software. The best way to see what is different between Python 3.x versions is to consult the official Python "what's new" documentation. Furthermore, teams may modify their Jenkins and/or Travis environments to run automated tests in an upgraded Python environment and make sure that tests are passing.

In addition to upgrading any Python software, teams must also ensure that the Python version used in provided software environments are all consistent. This includes:

  • conda environments (i.e. environment.yml)
  • Package environments (i.e. requirements.txt, setup.py, sphinx documentation)
  • Continuous integration environments (i.e. Jenkins or Travis configuration files).

Make sure to update any of these files as necessary.

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