Why is Python installed to /usr/local/bin/python3?

[hwittenborn]

I just got started using the image, and I noticed that Python is installing to files like /usr/local/bin/python3 by default. Is there any reason for doing so?

The issue mostly came into play when I was using a #!/usr/bin/python3 shebang at the top of one of my scripts, after which I noticed imports were just straight-up not working after installing some dependencies with Pip.

It's not really an issue if you can figure out how to fix the issue (running type python3 manually in a container revealed the issue for me), though I suspect that some users might end up spending quite a bit of time on it.

Perhaps there could be symlinks to /usr/local/bin for the Python executables (i.e. /usr/bin/python3 to /usr/bin/python3.10 on the current latest tag)? I'm seeing that they go to Debian-installed executables by default (/usr/bin/python3 goes to /usr/bin/python3.9 at least), but I don't see any benefit provided by that.

[wglambert]

python/3.9/buster/Dockerfile

Lines 9 to 10 in 2bf869e

	# ensure local python is preferred over distribution python
	ENV PATH /usr/local/bin:$PATH

It ensures the local Python is preferred over the distribution's
https://github.com/docker-library/docs/tree/master/python#multiple-python-versions-in-the-image

[yosifkit]

/usr/local/ is used to prevent system packages from accidentally overwriting the source installed python provided by the image (https://refspecs.linuxfoundation.org/FHS_3.0/fhs/ch04s09.html). If we change the symlinks (via something like dpkg-divert), then we could likely break system tools (like apt) by providing an incompatible python3.

Rather than assuming the location of the python3 executable in your scripts, you can use env to find the preferred executable. So I think the universal shebang would be #!/usr/bin/env python3.