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Virtualenvs solve not having separate workspace-local package installations, not a lack of versioned imports. Versioned imports are not a good solution to sepa

Virtualenvs solve not having separate workspace-local package installations, not a lack of versioned imports. Versioned imports are not a good solution to separate installations of packages: code is harder to upgrade, cluttered, and encouraged to depend on specifics rather than contracts. There’s a reason every major language localizes their version pinning into a per-project dependencies file (which can be anywhere on the spectrum between “contracts only semver ranges” and “checksummed/vendored lockfile”). And that’s before considering the troublesome behaviors that emerge when you permit importing multiple versions of the same library in the same program, if you want that too.

eru 2y ago
> And that’s before considering the troublesome behaviors that emerge when you permit importing multiple versions of the same library in the same program, if you want that too. Rust has versioned imports. So you can import different versions of the same module (at least in your transitive dependencies).
- zbentley 2y ago
  Yep. And while that’s not something I’d call a mistake per se, it can be troublesome. What if a crate you depend on at different versions provides access to global state? What if a transitive embeds definitions from that crate into public contracts consumed by code using a different version? Rust offers mitigations or means of detection for those cases, but they still require thought and troubleshooting when they occur. Given Python’s lack of static typing and more-likely-to-be-nonexpert user base and usage patterns, I suspect that troublesomeness would not be a value-add for the Python platform.
  - eru 2y ago
    Well, for what it's worth, Rust's linter clippy likes to warn you about using different versions of the same crate. I think the warning is mostly formulated in terms of helping you reduce compile times, but your concerns about mutability might also be justified.

eru 2y ago

> And that’s before considering the troublesome behaviors that emerge when you permit importing multiple versions of the same library in the same program, if you want that too. Rust has versioned imports. So you can import different versions of the same module (at least in your transitive dependencies).

zbentley 2y ago
Yep. And while that’s not something I’d call a mistake per se, it can be troublesome. What if a crate you depend on at different versions provides access to global state? What if a transitive embeds definitions from that crate into public contracts consumed by code using a different version? Rust offers mitigations or means of detection for those cases, but they still require thought and troubleshooting when they occur. Given Python’s lack of static typing and more-likely-to-be-nonexpert user base and usage patterns, I suspect that troublesomeness would not be a value-add for the Python platform.
- eru 2y ago
  Well, for what it's worth, Rust's linter clippy likes to warn you about using different versions of the same crate. I think the warning is mostly formulated in terms of helping you reduce compile times, but your concerns about mutability might also be justified.