For not having to call 'source ...' in a Dockerfile, if you use the python executable from the virtualenv directly, then it will be as if you've activated that virtualenv.
This works because of the relative path to the pyenv.cfg file.
This works because of the relative path to the pyenv.cfg file.
Python sticks out for having the arrogance to think that it’s special, that “if you’re using Python you don’t need Docker, we already solved that problem with venv and conda”. And like, that’s cute and all, but I frequently need to package Python code and code in another language into one environment, and the fact that their choice for “containerizing” things (venv/conda) plays rudely with every other language’s choice (Docker) is really annoying.
If that's not good enough for you, you could do some devops stuff and build a docker container in which you compile Python.
I don't see where it is different from some npm project. You just need to use the available resources correctly.