When I'm in a docker container using the Python 3 version that comes with Debian - is there an easy way to swap it out for this version so I can test how my software behaves under 3.13?
Otherwise, there's always the excellent `pyenv` to use, including this person's docker-pyenv project [1]
[0] https://hub.docker.com/layers/library/python/3.13.0rc3-slim-... [1] https://github.com/tzenderman/docker-pyenv?tab=readme-ov-fil...
What I meant is: While I am already inside a container running Debian, can I ...
1: ./myscript.py
2: some_magic_command
3: ./myscript.py
I don't need to preserve 3.11. some_magic_command can wrack havoc in the container as much as it wants. As soon as I exit it, it will be gone anyhow.
The in a sense, the question is not related to Docker at all. I just mentioned that I would do it inside a container to emphasize that I don't need to preserve anything.
Pro tip: outside Docker, don’t ever use the OS’s own Python if you can avoid it.
This includes Homebrew's Python installation, which will update by itself and break things.
(Technically, I use uv now, but to the same ends.)
Why not?
You almost always want to develop in a virtualenv so you can install the exact versions of things you need without conflicting with the ones the OS itself requires. If you're abstracting out the site-packages directory anyway, why not take one more step and abstract out Python, too? Things like pyenv and uv make that trivially easy.
For instance, this creates a new project using Python 3.13.
$ uv init -p python3.13 foo
$ cd foo
$ uv sync
$ .venv/bin/python --version
Python 3.13.0rc2
You can get 95% of the same functionality by installing pyenv and using it to install the various versions you might want. It's also an excellent tool. Python's own built-in venv module (https://docs.python.org/3/library/venv.html) makes it easy to create virtualenvs anytime you want to use them. I like using uv to combine that and more into one single tool, but that's just my preference. There are many tools that support this workflow and I highly recommend you find one you like and use it. (But not pipenv. Don't pick that one.)
Yes, make a venv for each work project.
If you're doing work on a large Python app for production software, then using system Python isn't going to cut it.
Keeping the number of dependencies reasonable is probably the most important factor, rather than lines of code.
You want precompiled Python binaries. Use “uv” for this, rather than hacking it together with pyenv.
If you already have pyenv, use it. If you don't have pyenv or uv, install uv and use that. Either one is a huge upgrade over using the default Python from your OS.
One other advantage is that you know the provenance of the python executable when you build it yourself. Uv downloads a prebuilt exe from https://gregoryszorc.com/docs/python-build-standalone/main/ who is a very reputable, trusted source, but it's not the official version from python.org. If you have very strict security requirements, that may be something to consider. If you use an OS other than Linux/Mac/Windows on x86/ARM, you'll have to build your own version. If you want to use readline instead of libedit, you'll have to build your own version.
I am personally fine with those limitations. All of the OSes I regularly use are covered. I'm satisfied with the indygreg source security. The libedit version works fine for me. I like that I can have a new Python version a couple seconds after asking for uv. There are still plenty of reasons why you might want to use pyenv to build it yourself.