If you don't care which version of python it runs under, you do this:

    #!/usr/bin/env python

If you do, then `python2` or `python3` will be around, and you should specify them explicitly instead of `python`. I'm happy to be corrected on this one, but I always slap this at the top of my scripts:

    #!/usr/bin/env python3

I'm not aware of anywhere that wouldn't invoke a Python 3 interpreter if one is installed.

The original post just seems like one big faff.

My system doesn't have a `python`. On Ubuntu you need to install one of the `python-is-python2` or `python-is-python3` packages for the `python` command to be available.

  Command 'python' not found, did you mean:

    command 'python3' from deb python3
    command 'python' from deb python-is-python3

https://packages.ubuntu.com/focal/python-is-python3

All Debian based distros are this way, not just Ubuntu.

And a lot of non-Debian distros as well. Python 2 is officially retired after all.

PEP 394 (which is now superseeded) clearly states that "python" shall invoke python2 and not python3

https://www.python.org/dev/peps/pep-0394/

"The python command should always invoke Python 2 (to prevent hard-to-diagnose errors when Python 2 code is run on Python 3)."

So there was indeed a time where the mentioned scenario was possible.

Edit: love those people who got to downvote reality. At no point was python pointing to either 2 or 3 will-nilly, but there was always a PEP specifying best practice behaviour.

> "python" shall invoke python2 and not python3

The current version of PEP 394 says:

] If the python command is installed, it is expected to invoke either the same version of Python as the python3 command or as the python2 command.

] Distributors may choose to set the behavior of the python command as follows:

    python2,
    python3,
    not provide python command,
    allow python to be configurable by an end user or a system administrator.

The part you quoted is from the section "History of this PEP". Just before your quoted text is:

] This PEP originally provided a very simple mechanism ...

and just after it is:

] However, these recommendations implicitly assumed that Python 2 would always be available.

This historic advice is no longer recommended.

The change was made on July 5, 2019 - https://github.com/python/peps/commit/ae932bd6fd2c493d7d64ce... .

The PEP is not superseded, still active. You got this quote from the "history of this PEP" section. This is not what the PEP currently mandates and it hasn't for 2.5 years: https://github.com/python/peps/pull/989

That was not the point. There was a time where the PEP specified that "python" means "python2" and it was indeed possible to have no "python" but still a Python (3) installation.