Pick a Python version, manage it with uv (or pyenv)

Why this matters

Python 3.12+ is the version every new project should target — it's faster (perf project), it has structural pattern matching from 3.10, exception groups from 3.11, and per-interpreter GIL changes from 3.12. The wrong instinct is to use whatever python3 is on your Mac (often a stale 3.9). The right instinct: install a version manager (uv or pyenv), pin per-project, and treat 'system Python' as untouchable. uv (from Astral, the ruff team) is the 2026 winner — it bundles version mgmt, virtualenvs, dep resolution, and pip into one ~25 MB binary that's 10–100× faster than pip.

Demo

uv is a next-generation Python package manager written in Rust that replaces pip, pip-tools, and virtualenv in a single binary. It resolves and installs dependencies 10-100× faster than pip and produces a lockfile (uv.lock) that pins the exact version of every package in the transitive graph. Pinning a Python version with uv python pin 3.12 ensures that every developer and CI run uses the same interpreter, eliminating 'works on my machine' failures caused by minor version differences.

Try it yourself

1. Install uv. Run uv --version to confirm.
2. Install Python 3.12 via uv python install 3.12 and pin it in a fresh dir with echo "3.12" > .python-version.
3. Run uv run python -c "import sys; print(sys.version)" and confirm you got 3.12.
4. Inspect which python vs uv run which python. Note that uv keeps a project-scoped Python separate from your shell's.

Prompt your AI

Use these three in order. Each builds on the one before.

1. Basics & terminology

In one paragraph, explain why I shouldn't use the `python3` that ships with macOS or Ubuntu — and what 'pin Python per project' actually means.

2. Why it works (the mechanism)

Walk me through what `uv python install 3.12` does: where the interpreter is downloaded from, where it's stored, how `uv run` finds it.

3. Advanced — application & what's next

Compare uv, pyenv, conda, and Docker for Python version management. Pick a winning strategy for a 5-person team shipping a FastAPI service in 2026 and defend it.

References

• uv (Astral)
• Python 3.12 What's New
• PEP 8 — Style Guide