[Python-Dev] PEP 394 update proposal: Allow changing the python command in some cases (original) (raw)

Petr Viktorin encukou at gmail.com
Wed Apr 25 15:10:10 EDT 2018

• Previous message (by thread): [Python-Dev] Meta-question about this mailing list
• Next message (by thread): [Python-Dev] PEP 394 update proposal: Allow changing the `python` command in some cases
• Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]

Hello, In Fedora, I found that PEP 394's strict recommendation that python points to python2 is holding us back. From discussions on Zulip and elsewhere it's clear that this recommendation is not changing any time soon, but I would like to officially relax it in several cases.

The problems are:

• For developers that are not following the language's development, the fact that python invokes python2 sends a strong signal that 2 is somehow the preferred version, and it's OK to start new projects in it.
• Users and sysadmins that do want to “live in the future” are switching the symlink to python3 themselves. We would like to give them a supported, documented way to do so -- and make surer they're aware of the caveats.
• The python command is still not available out-of-the box on macOS, so it didn't completely live up to the expectation of being the cross-platform way to launch 2/3 source compatile scripts.
• python in the shebang line can mean either that a script is carefully written to be 2/3 compatible, or that the author/maintainer is lazy or unaware of the recommendations. While Fedora guidelines have long banned the unversioned command, we feel that the only way to enforce that guidelines is to provide environments where the python command does not work (unless explicitly installed).

To help solve these, I would like to relax recommendations on the Unix python -> python2 symlink in these cases:

• Users and administrators can, by a deliberate action, change python to invoke Python 3. (Activating a venv counts as such an action, but so would e.g. using alternates, installing a non-default overriding package, or replacing /usr/bin/python.)
• In controlled environments where being explicit is valued more than user experience (test environments, build systems, etc.), distributions can omit the python command even when python2 is installed.

I have filed these changes as a pull request here:

https://github.com/python/peps/pull/630

The PR also spells out several other things, which I felt were hidden between the lines -- but correct me if you disagree with my reading.

• Previous message (by thread): [Python-Dev] Meta-question about this mailing list
• Next message (by thread): [Python-Dev] PEP 394 update proposal: Allow changing the `python` command in some cases
• Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]

More information about the Python-Dev mailing list