Pinning direct dependencies with == is a great step towards creating reproducible environments. To further improve this and ensure long-term maintainability, consider using a tool like pip-tools.

With pip-tools, you would maintain a requirements.in file with your high-level dependencies. Running pip-compile would then automatically generate a fully-pinned requirements.txt file, including all transitive dependencies (like altair).

This approach automates pinning, simplifies updates, and makes the entire dependency tree explicit and locked. It's a valuable practice for ensuring robust and maintainable dependency management as the project grows.