uv: The Modern Python Package Manager

uv is a next-generation tool for managing Python dependencies. Written in Rust by Astral, it is 10–100× faster than pip and replaces several tools at once: pip, venv, pyenv, and pip-tools.

Why Another Package Manager

Standard pip works, but it’s slow and imprecise. Installing Django takes 30–60 seconds — uv does it in 1–2 seconds. But speed isn’t the main point.

The main point is reproducibility. pip install without a lockfile can install different versions on different machines. uv generates uv.lock — a deterministic file with exact versions of all packages, including transitive dependencies. On any machine, uv sync produces an identical environment.

Installation

On Mac/Linux:

curl -LsSf https://astral.sh/uv/install.sh | sh

On Windows (PowerShell):

powershell -ExecutionPolicy ByPass -c "irm https://astral.sh/uv/install.ps1 | iex"

After installation, restart your terminal:

uv --version  # uv 0.5.x

Creating a Project

uv init my-project    # creates a directory with pyproject.toml and .venv
cd my-project

What gets created automatically:
- pyproject.toml — project description and dependencies
- .python-version — pinned Python version
- hello.py — starter file
- .venv/ — virtual environment

Adding Dependencies

uv add anthropic              # add a dependency
uv add httpx rich environs    # add several at once
uv add pytest --dev           # dev dependency (not in prod)
uv remove requests            # remove a dependency

Dependencies are automatically written to pyproject.toml and locked in uv.lock.

Running Code

uv run python main.py     # run in the virtual environment
uv run pytest             # run tests
uv run ruff check .       # run any tool

uv run activates the correct environment automatically — no need to run source .venv/bin/activate.

Lockfile and Reproducibility

Commit uv.lock to Git. It guarantees that all team members and CI use identical versions.

uv sync              # install exactly from the lockfile
uv sync --dev        # including dev dependencies

Comparison with pip + venv

pyproject.toml

The standard project description format (PEP 517/518). uv creates and updates it automatically:

[project]
name = "my-project"
version = "0.1.0"
requires-python = ">=3.12"
dependencies = [
    "anthropic>=0.40.0",
    "rich>=13.0.0",
    "environs>=11.0.0",
]

[tool.uv]
dev-dependencies = [
    "pytest>=8.0.0",
    "ruff>=0.8.0",
]

Tip: .python-version

The .python-version file pins the Python version for the project. uv reads it and downloads the required version automatically if needed — no pyenv required.

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