Comment by Galanwe
Well, first, this a purposefully contrived example, that pretty much does not happen in real life scenarios. So you're pretty much acknowledging that there is no real problem by having to resort to such length.
Second, what exactly would you like to happen in that instance? You want to have, in a single project, the same library but at different and conflicting versions. The only way to solve that is to disambiguate, per call site, each use of said library. And guess what, that problem exist and was solved 30 years ago by simply providing different package names for different major version. You want to use both gtk 1 and gtk 2 ? Well you have the "gtk" and "gtk2" package, done, disambiguated. I don't think there is any package manager out there providing "gtk" and having version 1 and 2, it's just "gtk" and "gtk2".
Now we could design a solution around that I guess, nothing is impossible in this brave new world of programing, but that seems like a wasted effort for not-a-problem.
Maybe this doesn’t happen in Python, but I find that hard to believe. This is a common thing in Rust, where cargo does support compiling with multiple versions of the same crate. If I have dependency X that depends on version 1.x of crate Z, and dependency Y which depends on version 2.x, cargo will compile BOTH versions of crate Y, and handle the magic of linking dependencies X and Y to their own, different copies of this common dependency.