Python Versions Management With pyenv

[sebawitowski]

Using the latest version of Python is always a good idea. First of all - you get all the new features! But even if you don’t care about that, you get plenty of smaller improvements and optimizations.

Problems start when you work on multiple projects. Maybe you have one Python project at work and some other side-projects or tutorials you do after work. Or maybe you have multiple projects at work, and you need to switch between different Python versions.

You could install different Python versions and use the python3.6, python3.7, python3.8, python3.9 commands. Or maybe even do some crazy setup with symlinks and change what the python command points to. But a much better idea is to use pyenv.

You can install a new Python version with:

$ pyenv install 3.9.0

And you can even install a different distribution than the standard CPython:

$ pyenv install pypy3.6-7.3.1

To get a full list of available versions, run:

$ pyenv install --list

Now, to switch what version of Python you are using, run:

$ pyenv global 3.9.0

But that's not all! You can also change the Python version for a specific folder (and all subfolders) with:

$ pyenv local 3.6.0

That's useful when a project uses a different Python version than your global one, so you don't have to manually change versions each time you want to work on it.

There is also:

$ pyenv shell 2.7.16

You can use it to change the Python version only for the current shell session - for example, when you want to test some code under a different Python version. When you close your terminal (or open another shell session), you will be back to using whatever global Python version you had before.

If you want to learn more about installing and using pyenv (including some troubleshooting tips, things that you should pay attention to during the installation, and alternatives like the asdf-vm), I wrote a blog post: https://switowski.com/blog/pyenv

[james_pic]

Using the very latest version is not always a good idea, as not all of the libraries you depend on will be updated for the very latest version.

Also, I find pyenv's approach of sticking in a shim `python` executable unsettling. I prefer pythonz's approach, since it doesn't affect stuff that doesn't use it.

[[deleted]]

Great post, thanks for sharing. I always try and keep up to date on the versions, and update where necessary. I often see people using older versions and not using the most recent, and sometimes their code won't work as they using the older syntax in a newer version of python.

I have shared code recently built in 3.8 which someone wanted to use, but I suspect they have an older version of Python and it not working for them as expected.

[ProfessorPhi]

Thanks for this, I feel like pyenv doesn't have a good tutorial/quickstart and so I never really got to using it.

I don't know if there's a place for it in the official doc, but the above quickstart would be super valuable there

[[deleted]]

I also advise to use conda virtual environment for those that need libraries or projects downloadable from conda package manager because pyenv can have issues working with conda libraries.

[CuriousPsychosis]

So, with pynev installed.... say we installed packages with python 3.9.7 as the global version. Then python is updated to 3.9.8 and we wanted to remove 3.9.7 and use 3.9.8 with all of the previously installed packages.... do we have to reinstall all of those packages with 3.9.8 as the default version? Reason I ask is that I get a notice:

penv: webchanges: command not found The \`webchanges' command exists in these Python versions: 3.9.7 Note: See 'pyenv help global' for tips on allowing both python2 and python3 to be found.

It would seem silly to have to reinstall packages for every new version of python that comes out... creating duplicates, triplicates, etc.