[arcatek]

It's not about the package manager, it's about the runtime. Python isn't able to support this pattern with its resolution pipeline, so package managers have to resort to do the work to dedupe versions.

By contrast Node.js has built-in capabilities that make this possible, so package managers are able to install multiple versions of the same package without that issue.

[stabbles]

It's not just that, it's also a filesystem layout issue. If you install everything in `/usr` or `<venv>/lib/pythonX.Y/site-packages` you cannot have two versions / variants of the same package installed concurrently.

For that you need one prefix per installation, which is what Nix, Guix, and Spack do.

[avsm]

The runtime can also use mount namespaces to support concurrent installations. Or, if there is a compilation step, the linker can not expose symbols for clashing libraries and just resolve them within the dependency chain.

The package calculus allows all of these to specified cleanly in a single form.