Uv

uv - Python Package and Project Manager

Contents

• Core Concept: uv run
• Quick Reference
• Common Workflows
• Dependency Management
• Python Version Management
• Scripts with Inline Dependencies
• Troubleshooting
• References

Core Concept: uv run

ALWAYS use uv run instead of bare python in uv-managed projects.

uv run automatically:

• Creates/updates the virtual environment
• Installs project dependencies
• Executes commands in isolation

# Run Python scripts
uv run script.py

# Run CLI tools
uv run pytest
uv run ruff check .

# Run Python modules
uv run python -m mymodule

Quick Reference

Essential Commands

Decision Tree

Common Workflows

1. Create New Project

uv init my-project        # Application
uv init --lib my-library  # Library
uv init                   # In current directory
uv init --python 3.12     # Specify Python version

Creates: pyproject.toml, .python-version, README.md, src/

2. Add Dependencies

uv add requests                    # Runtime
uv add 'httpx>=0.25,<0.27'        # With constraints
uv add --dev pytest pytest-cov    # Development
uv add --optional docs sphinx     # Optional group

3. Run Tests and Tools

uv run pytest
uv run pytest --cov
uv run ruff check .
uv run mypy src/

4. Update Dependencies

uv lock --upgrade               # Upgrade all
uv lock --upgrade-package numpy # Upgrade one
uv sync                         # Apply changes

5. Build and Publish

uv build                        # Build package
uv publish                      # Publish to PyPI

Dependency Management

Adding Dependencies

Temporary Dependencies

Use --with for one-off operations without modifying pyproject.toml:

uv run --with httpx python -c "import httpx"
uv run --with rich --with httpx script.py

Syncing Environment

uv sync              # Sync all
uv sync --no-dev     # Without dev deps
uv sync --all-extras # Include optional groups

Python Version Management

uv python install 3.12    # Install version
uv python list            # List available
uv python pin 3.12        # Pin for project
uv python find            # Find installations

Scripts with Inline Dependencies

Scripts can declare their own dependencies, isolated from the project:

# /// script
# dependencies = [
#   "requests<3",
#   "rich",
# ]
# requires-python = ">=3.12"
# ///

import requests
import rich

Managing Script Dependencies

uv init --script analyze.py --python 3.12   # Create script
uv add --script analyze.py pandas           # Add dependency
uv run analyze.py                           # Run (uses inline deps)
uv lock --script analyze.py                 # Lock dependencies

Note: Scripts with inline metadata ignore project dependencies.

Tools Without Installation

uvx ruff check .          # Run tool ephemerally
uvx black --check .
uv tool install ruff      # Install globally
uv tool list              # List installed tools

Troubleshooting

Command Not Found After uv add

Problem: Added package with CLI, but command doesn't work.

Solution: Use uv run:

uv add ruff
uv run ruff check .  # Not just "ruff check ."

Environment Out of Sync

Problem: Dependencies changed but environment hasn't updated.

Solution:

uv sync

Wrong Python Version

Problem: Project requires different Python.

Solution:

uv python install 3.12
uv python pin 3.12

Script Ignores Project Dependencies

Problem: Script with inline metadata doesn't use project packages.

Solution: This is intentional. Either:

• Remove inline metadata to use project deps
• Add needed deps to script's inline metadata

Best Practices

1. Always use uv run - Don't manually activate venvs
2. Commit uv.lock - Ensures reproducible builds
3. Pin Python versions - Use uv python pin
4. Use --with for experiments - Test deps without modifying pyproject.toml
5. Use uvx for one-off tools - Don't pollute project deps
6. Let uv manage envs - Avoid manual pip installs

References

Project References

• CLI Reference - Complete command documentation

External Resources

• uv Documentation
• CLI Reference
• GitHub

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