On Linux, You Have To Manually Change The Shebang On x.py From Python To Python3

[nishantc1527]

Currently, this is the first line in x.py.

#!/usr/bin/env python

However, on linux since it is python3 by default when you install python (at least on centos), I have to manually change it to this every time I clone this repository.

#!/usr/bin/env python3

Is there some way that there is an automated way to detect this? If not, maybe you can update the docs because it took me a while to figure out what was going wrong.

[tesuji]

Do you mean that by default CentOS use python as python3?

[Mark-Simulacrum]

There is unfortunately not a universal python shebang - windows never has python3 IIRC, and Ubuntu at least doesn't by default have a python these days.

If you have concrete proposals on how to make this work, I would love to hear them - a compiler team MCP is the way to go to propose such a change.

[mati865]

@nishantc1527 You can either use python3 x.py or set python3 as the default version using this official guide: https://developers.redhat.com/blog/2018/11/14/python-in-rhel-8/

[K900]

#!/usr/bin/env python3 should be a universal shebang for Python 3 specifically - I'm not aware of any distributions that actively remove the python3 symlink, and the Windows launcher understands it as well.

[mati865]

@K900 Rust supports both Python 2 and Python 3.

[nishantc1527]

If there isn't an automated way to detect this (at least I can't thing of anything), then can the team update the documentation on how to install rust from source? It took me a while to figure out what was happening, and I believe someone smarter than me (which includes a lot of people) can get confused to.

[RalfJung]

Cc #71818: latest Ubuntu also does not have python any more by default, it seems.

So longer-term, I think it is clear that this should become python3 eventually, as more and more distros no longer install Python 2 by default. The question is when is the right time for Rust to switch its shebang.

[K900]

An alternative option would be to provide some sort of a wrapper script (./x.sh?) that effectively just does

PYTHON=`which python3 || which python2 || which python` 2>/dev/null
"${PYTHON}" ./x.py $@

[jyn514]

Closing as duplicate of #71818