@rooster I've used a few distributions in my time, having started with Red Hat in 1996 and migrated over to Slackware.
Python stuff: the best support I've seen so far for #Python has been in #Gentoo. You can have multiple Python interpreters installed side-by-side (including pypy), when you install a Python module that's packaged as a Gentoo package, it will install that module for each interpreter you have installed.
I've not seen that in other distributions. That said, maintenance can be cumbersome.
That said, the permutations and combinations of compiler toolchain and libraries can give rise to C++ headaches. Some upstream projects refuse to support Gentoo.
@esther suggested FreeBSD… the BSD space in general is worthy of a look. Very good (NOT Linux-based) operating systems with a long history. There's also #NetBSD (focussed on portability), #OpenBSD (NetBSD fork focussed on security), #DragonFlyBSD (FreeBSD fork, not tried it).
Lots have suggested #Debian -- a fine choice if you have a regular desktop computer and don't want to spend your day compiling. Widely supported and understood.
I won't comment on #Fedora: my memories of it were circa 2004 or so.
I did try #CentOS in a VM (actually needed it because Tridium's development environment requires it), and found it a very bloated OS.
#Ubuntu isn't bad if you need hand-holding, but I do find it too is a very "heavy" OS, even with a lightweight desktop. Quite pre-occupied with "snap" packages. I use it at work because that's the company standard (with the FVWM desktop, which confuses colleagues no end).
Won't comment on #OpenSuSE -- I do recall using #SuSE Linux years ago, and it too, was a very "big" OS, but once again, we're talking 20 years ago or more.
#Slackware is still kicking, probably the longest-running Linux distribution there is. (The one that came before it was #Yggdrasil) Lightweight, but be prepared for it to emulate Linux From Scratch when something you want isn't shipped in the packages.
Speaking of which, #LinuxFromScratch is an option if you're a masochist. 
If you think Gentoo is hard, this is a LOT of work! You are the package manager, and software repo!
If you want small, and binary compatibility isn't an issue, #AlpineLinux is worthy of a look. Gentoo-ish feel (with OpenRC), but binary packages. A VM can be installed in 50MB!
If you really want small for an embedded project, #BuildRoot is worth a look.
I've heard good things about #ArchLinux but never tried it, so can't comment further.
That was a long post, but hopefully that gives you some ideas.
