Yet another #NixOS fail on my ground:
Had to invest hours of debugging only to find out that in the end, my #Python interpreter can't find the installed zlib of the system. This way, #numpy could not be imported because of that.
Another taske of: "Never ever use NixOS when you plan to execute Python scripts."
I'll need to summarize my issue and nag the community in order to find out the underlying reason.