uv

uv is an extremely fast Python package and project manager written in Rust. It replaces pip, pip-tools, pipx, pyenv, virtualenv, and poetry.

When to Use uv

Always use uv for Python work, especially if you see:

• The uv.lock file
• uv headers in requirements* files (“This file was autogenerated by uv”)

Don’t use uv in projects managed by other tools:

• Poetry projects (poetry.lock)
• PDM projects (pdm.lock)

Workflows

Scripts

Use when: Running single Python files and standalone scripts.

uv run script.py                      # Run a script
uv run --with requests script.py      # Run with additional packages
uv add --script script.py requests    # Add inline dependencies to script

Projects

Use when: There is a pyproject.toml or uv.lock

uv init                   # Create new project
uv add requests           # Add dependency
uv add --dev pytest       # Add dev dependency
uv remove requests        # Remove dependency
uv sync                   # Install from lockfile
uv run <command>          # Run in project environment
uv run python -c ""       # Run Python in project environment
uv run -p 3.12 <command>  # Run with specific Python version

Tools

Use when: Running CLI tools (ruff, pytest, mypy) without installation.

uvx <tool> <args>            # Run tool without installation
uvx <tool>@<version> <args>  # Run specific version
uvx ruff check .             # Example: run ruff

Important: Only use uv tool install when explicitly requested.

Pip Interface

Use when: Legacy workflows with requirements.txt, no uv.lock present.

uv venv                                # Create virtual environment
uv pip install -r requirements.txt     # Install from requirements
uv pip compile requirements.in -o requirements.txt  # Compile deps
uv pip sync requirements.txt           # Sync environment
uv pip compile --universal requirements.in -o requirements.txt  # Cross-platform

Prefer uv init for new projects over pip interface.

Workspaces

Workspaces manage multiple related packages in a monorepo structure.

Configuration

# Root pyproject.toml
[tool.uv.workspace]
members = ["packages/*", "apps/*"]
exclude = ["packages/legacy"]

[tool.uv.sources]
# Local package references
mylib = { workspace = true }
shared = { path = "../shared", editable = true }

# Git sources
mypackage = { git = "https://github.com/org/repo", branch = "main" }

Structure

my-workspace/
├── pyproject.toml          # Root workspace config
├── uv.lock                  # Single lockfile for all packages
├── packages/
│   ├── core/
│   │   └── pyproject.toml  # [project] with dependencies
│   └── utils/
│       └── pyproject.toml
└── apps/
    └── api/
        └── pyproject.toml

Commands

uv sync                           # Sync all workspace packages
uv sync --package myapp           # Sync specific package
uv run --package myapp pytest     # Run in specific package context
uv add requests --package myapp   # Add dep to specific package
uv lock                           # Update workspace lockfile

Cross-Package Dependencies

# apps/api/pyproject.toml
[project]
dependencies = ["core", "utils"]

[tool.uv.sources]
core = { workspace = true }
utils = { workspace = true }

Python Version Management

uv python install 3.12           # Install Python version
uv python list --only-installed  # List installed versions
uv python pin 3.12               # Pin version for project
uv python install 3.12 --default # Set as system default

Common Patterns

Don’t use pip in uv projects

# ❌ Bad
uv pip install requests

# ✅ Good
uv add requests

Don’t run python directly

# ❌ Bad
python script.py
python -c "..."

# ✅ Good
uv run script.py
uv run python -c "..."

Don’t manually manage environments

# ❌ Bad
python -m venv .venv
source .venv/bin/activate

# ✅ Good
uv run <command>

Running with specific Python

# ❌ Bad
python3.12 -c "..."

# ✅ Good
uvx python@3.12 -c "..."
uv run -p 3.12 <command>

Migration

From pyenv

pyenv install 3.12       → uv python install 3.12
pyenv versions           → uv python list --only-installed
pyenv local 3.12         → uv python pin 3.12
pyenv global 3.12        → uv python install 3.12 --default

From pipx

pipx run ruff            → uvx ruff
pipx install ruff        → uv tool install ruff
pipx upgrade ruff        → uv tool upgrade ruff
pipx list                → uv tool list

From pip/pip-tools

pip install package      → uv pip install package
pip-compile req.in       → uv pip compile req.in
pip-sync req.txt         → uv pip sync req.txt
virtualenv .venv         → uv venv

Best Practices

Project Setup:

1. Use uv init for new projects
2. Use uv add for dependencies (not pip install)
3. Commit uv.lock to version control
4. Use uv sync to reproduce environments

Workspaces:

1. Define members with glob patterns: packages/*
2. Use workspace = true for internal dependencies
3. Single uv.lock at root manages all packages
4. Run commands with --package for specific contexts

Scripts:

1. Use uv run script.py instead of python script.py
2. Use --with for ad-hoc dependencies
3. Use uv add --script for persistent script dependencies

Documentation

• https://docs.astral.sh/uv/llms.txt