A one-liner to upgrade your virtualenvs

This blog is powered by Nikola, a Python-based static blog compiler, which I've installed in a Python virtualenv to separate it from the system-wide Python installation of my notebook. Updates of the major version of Python (like from 3.6 to 3.7) inevitably break these virtualenvs, and I have so far accepted that there's no other way to get them back than to rebuild them from scratch. In fact, that's what you get to hear even from experienced Linux developers.

The recent update to Python 3.7 brought that topic back to my attention, and I kind of lost my patience. I just couldn't accept that there shouldn't be a better way, and indeed found a solution for those using the venv module of Python 3.3+:

python -m venv --upgrade <path_of_existing_venv>

Despite the fact that I'm using virtualenv instead of venv, this command worked exactly as I had hoped. ☺

The virtualenv can now be updated as usual. Well, almost – both pip and pip-tools got a lot more conservative and actually have to be told explicitly that they really should upgrade to the latest version. For a particular package, that looks like this:

pip install --upgrade Nikola --upgrade-strategy=eager

A rather weird behavior, if you ask me, but what do I know. ☺

Back to our virtualenv. To really, genuinely and truly update all requirements, the following sequence of commands is necessary:

pip install --upgrade setuptools
pip install --upgrade pip
pip install --upgrade pip-tools
pip-compile --rebuild --upgrade --output-file requirements.txt requirements.in
pip-sync requirements.txt

The update to Nikola 8.0.0 broke my old theme (based on bootstrap2), and it was about time: too many things were not working as desired. I'm now using an essentially unmodified bootblog4, as before with Kreon as the main font, and Muli for the headlines (from 15.12.2018: Oswald for the latter).