uv-python-manager

UV is the modern standard for Python package and project management in 2025, delivering 10-100x speed improvements while unifying pip, virtualenv, pyenv, poetry, and pipx into a single Rust-based tool.

When to Use This Skill

Use this skill when:

•Creating new Python projects
•Managing dependencies and lockfiles
•Setting up virtual environments
•Installing or switching Python versions
•Building or publishing packages
•Optimizing CI/CD pipelines
•Migrating from pip, poetry, or other tools
•Creating portable Python scripts
•Working with Docker containers

Core Principles

•Project-first workflow: Use uv init and uv add instead of manual configuration
•Lock file discipline: Always commit uv.lock for reproducibility
•Universal execution: Use uv run instead of manual environment activation
•Version pinning: Use .python-version for team consistency
•Fast by default: Leverage caching and parallel operations (8-100x faster than pip)

Quick Start

Installing UV

bash

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

# Windows PowerShell
powershell -c "irm https://astral.sh/uv/install.ps1 | iex"

# Update UV
uv self update

Creating a New Project

bash

# Initialize project (creates pyproject.toml, .python-version, .gitignore)
uv init my-project
cd my-project

# Add dependencies
uv add requests fastapi pandas

# Add development dependencies
uv add --dev pytest ruff mypy

# Add to custom groups
uv add --group docs sphinx
uv add --group test pytest-cov

# Run code (auto-syncs environment)
uv run python main.py
uv run pytest

Essential Commands Reference

Project Lifecycle

bash

uv init [name]              # Create new project with structure
uv add <package>            # Add dependency (updates pyproject.toml + uv.lock)
uv add --dev <package>      # Add development dependency
uv add --group <name> <pkg> # Add to custom dependency group
uv remove <package>         # Remove dependency
uv sync                     # Install/sync all dependencies
uv sync --frozen            # Sync without updating lock (CI mode)
uv sync --no-dev            # Production install (exclude dev deps)
uv run <command>            # Run command in project environment
uv build                    # Build distribution packages
uv publish                  # Publish to PyPI

Python Version Management

bash

uv python install 3.12      # Install Python version
uv python install 3.11 3.12 # Install multiple versions
uv python list              # List installed Python versions
uv python pin 3.12          # Pin project to Python version
uv python find              # Show active Python version

Virtual Environments

bash

uv venv                     # Create virtual environment (.venv/)
uv venv --python 3.12       # Create with specific Python version
uv venv my-env              # Create with custom name

Lock File Management

bash

uv lock                     # Update lockfile from pyproject.toml
uv lock --upgrade           # Upgrade all dependencies
uv lock --upgrade-package <pkg>  # Upgrade specific package
uv lock --check             # Verify lock is current (CI check)
uv export --format requirements-txt > requirements.txt  # Export format

Tool Management (replaces pipx)

bash

uvx <tool>                  # Run tool temporarily (no install)
uvx ruff check .            # Example: run ruff once
uv tool install <tool>      # Install tool globally
uv tool list                # List installed tools
uv tool uninstall <tool>    # Remove global tool

Maintenance

bash

uv cache clean              # Clean cache
uv cache dir                # Show cache location
uv self update              # Update UV itself

Project Structure Best Practices

Standard Layout

code

project/
├── .git/
├── .gitignore          # Auto-generated by uv init
├── .python-version     # Python version pin (COMMIT THIS)
├── README.md           # Setup instructions
├── pyproject.toml      # Project configuration (COMMIT THIS)
├── uv.lock             # Universal lockfile (COMMIT THIS)
├── .venv/              # Virtual environment (DO NOT COMMIT)
├── src/
│   └── package/
│       ├── __init__.py
│       └── main.py
└── tests/
    └── test_main.py

pyproject.toml Structure

toml

[project]
name = "my-app"
version = "0.1.0"
description = "Application description"
readme = "README.md"
requires-python = ">=3.11"
dependencies = [
    "requests>=2.31.0,<3.0.0",      # Range with upper bound
    "pandas>=2.0.0",                 # Minimum version
    "fastapi[standard]>=0.115.0",   # With extras
]

[project.optional-dependencies]
plotting = ["matplotlib>=3.7.0", "seaborn>=0.12.0"]
database = ["sqlalchemy>=2.0.0", "psycopg2-binary>=2.9.0"]

[dependency-groups]
dev = ["pytest>=8.0.0", "ruff>=0.3.0", "mypy>=1.8.0"]
test = ["pytest-cov>=4.1.0", "pytest-asyncio>=0.23.0"]
docs = ["sphinx>=7.0.0", "sphinx-rtd-theme>=2.0.0"]

Key Workflows

Dependency Management

Adding dependencies:

bash

# Single package
uv add requests

# Multiple packages
uv add requests pandas numpy

# With version constraints
uv add "fastapi>=0.115.0,<1.0.0"

# With extras
uv add "fastapi[standard]"

# Development dependencies
uv add --dev pytest ruff mypy

# Optional dependency groups
uv add --optional plotting matplotlib seaborn

Managing versions:

bash

# Upgrade all dependencies
uv lock --upgrade

# Upgrade specific package
uv lock --upgrade-package requests

# Pin to latest compatible versions
uv add requests --upgrade

Running Code

Always use uv run instead of activating environments:

bash

# Run Python scripts
uv run python script.py
uv run python -m mymodule

# Run installed tools
uv run pytest
uv run ruff check .
uv run mypy src/

# Run with specific Python version
uv run --python 3.12 python script.py

# Pass arguments
uv run pytest tests/ -v --cov

Why uv run is better:

•Auto-syncs environment before running
•Works cross-platform without activation scripts
•Ensures reproducibility
•Handles environment discovery automatically

Inline Script Dependencies (PEP 723)

Create portable single-file scripts:

python

#!/usr/bin/env -S uv run
# /// script
# requires-python = ">=3.11"
# dependencies = [
#     "requests",
#     "rich",
# ]
# ///

import requests
from rich import print

response = requests.get("https://api.github.com")
print(response.json())

Run with: uv run script.py (automatically installs dependencies)

Python Version Management

Project-level pinning:

bash

# Pin Python version for project
uv python pin 3.12

# This creates .python-version file
# Always commit this file to git

# UV will automatically use this version
uv run python --version

Installing Python versions:

bash

# Install specific version
uv python install 3.12

# Install multiple versions
uv python install 3.11 3.12 3.13

# List available versions
uv python list --all-versions

# List installed versions
uv python list

CI/CD Integration

GitHub Actions example:

yaml

name: CI
on: [push, pull_request]

jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      
      - name: Set up UV
        uses: astral-sh/setup-uv@v6
        with:
          version: "0.9.5"  # Pin UV version
          enable-cache: true
      
      - name: Set up Python
        run: uv python install
      
      - name: Install dependencies
        run: uv sync --frozen  # Use --frozen in CI
      
      - name: Check lock file is current
        run: uv lock --check
      
      - name: Run tests
        run: uv run pytest
      
      - name: Run linting
        run: uv run ruff check .

Docker optimization:

dockerfile

FROM python:3.12-slim

# Install UV
COPY --from=ghcr.io/astral-sh/uv:latest /uv /usr/local/bin/uv

# Set working directory
WORKDIR /app

# Copy dependency files
COPY pyproject.toml uv.lock ./

# Install dependencies with caching
RUN --mount=type=cache,target=/root/.cache/uv \
    uv sync --frozen --no-dev

# Copy application code
COPY . .

# Compile bytecode for faster startup
ENV UV_COMPILE_BYTECODE=1

# Run application
CMD ["uv", "run", "python", "-m", "myapp"]

Multi-stage Docker build:

dockerfile

# Stage 1: Build
FROM python:3.12-slim AS builder
COPY --from=ghcr.io/astral-sh/uv:latest /uv /usr/local/bin/uv
WORKDIR /app
COPY pyproject.toml uv.lock ./
RUN --mount=type=cache,target=/root/.cache/uv \
    uv sync --frozen --no-dev --no-editable

# Stage 2: Runtime
FROM python:3.12-slim
WORKDIR /app
COPY --from=builder /app/.venv /app/.venv
COPY . .
ENV PATH="/app/.venv/bin:$PATH"
ENV UV_COMPILE_BYTECODE=1
CMD ["python", "-m", "myapp"]

Migration from Existing Tools

From pip/pip-tools

bash

# Automated migration
uvx migrate-to-uv

# Or manual migration:
# 1. Create UV project
uv init

# 2. Import from requirements.txt
uv add -r requirements.txt
uv add --dev -r requirements-dev.txt

# 3. Commit new files
git add pyproject.toml uv.lock .python-version
git rm requirements.txt requirements-dev.txt

From Poetry

bash

# Automated migration
uvx migrate-to-uv

# UV reads pyproject.toml directly
# Just start using UV commands:
uv sync        # Replaces: poetry install
uv add pkg     # Replaces: poetry add pkg
uv run cmd     # Replaces: poetry run cmd

From virtualenv/venv

bash

# Old workflow:
# python -m venv .venv
# source .venv/bin/activate  # or .venv\Scripts\activate on Windows
# pip install -r requirements.txt

# New workflow:
uv init
uv add -r requirements.txt
uv run python script.py  # No activation needed

Troubleshooting

Common Issues

Lock file out of sync:

bash

# Error: "lock file is out of date"
uv lock  # Regenerate lock file

Python version not found:

bash

# Error: "Python 3.12 not found"
uv python install 3.12

Dependency conflicts:

bash

# Check resolution
uv lock --verbose

# Try upgrading
uv lock --upgrade

# Check specific package
uv lock --upgrade-package problematic-package

Cache issues:

bash

# Clean cache if corrupted
uv cache clean

# Show cache location
uv cache dir

Import resolution issues:

bash

# Ensure environment is synced
uv sync

# Force reinstall
uv sync --reinstall

Best Practices Checklist

•✅ Always commit uv.lock and .python-version to version control
•✅ Use uv sync --frozen in CI/CD pipelines
•✅ Add .venv/ to .gitignore and .dockerignore
•✅ Pin UV version in CI for consistency
•✅ Use uv run instead of manual environment activation
•✅ Specify requires-python range in pyproject.toml
•✅ Use dependency groups for dev tools, not optional-dependencies
•✅ Test with --resolution lowest for libraries
•✅ Enable bytecode compilation in Docker: UV_COMPILE_BYTECODE=1
•✅ Use cache mounts in Docker for faster builds
•✅ Run uv lock --check in CI to catch outdated lockfiles
•✅ Leverage inline script dependencies (PEP 723) for portable tools
•✅ Document UV setup in README for team onboarding

Performance Impact

UV achieves dramatic speed improvements:

•8-10x faster than pip without caching
•80-115x faster with warm cache
•Virtual environment creation: 100ms vs 8 seconds (python -m venv)
•Complex dependency resolution: seconds vs minutes
•CI/CD impact: 30-65% faster builds

This speed enables new workflows like re-syncing environments on every command invocation without performance penalties.

Advanced Topics

For more specialized use cases, see:

•WORKSPACE.md - Monorepo and multi-project setups
•PUBLISHING.md - Building and publishing packages
•SCRIPTS.md - Advanced script management patterns

Key Differences from Other Tools

vs pip

•Speed: 8-100x faster
•Lock files: Built-in universal lockfiles
•Python management: Can install Python versions
•Unified: Replaces pip + pip-tools + virtualenv

vs Poetry

•Speed: Significantly faster resolution and installation
•Lock files: Universal (cross-platform in one file)
•Simpler: Less configuration required
•Compatible: Reads Poetry's pyproject.toml

vs Conda

•Scope: Python-only (doesn't handle system dependencies)
•Speed: Much faster for Python packages
•Compatibility: Standard PyPI ecosystem
•Not a replacement: Use Conda when you need non-Python dependencies

Support and Resources

•Documentation: https://docs.astral.sh/uv/
•GitHub: https://github.com/astral-sh/uv
•Discord: Join Astral's community
•Changelog: https://github.com/astral-sh/uv/releases

Summary

UV standardizes Python development by unifying package management, environment management, Python version management, and script execution into a single fast tool. The key workflow is:

•uv init to create projects
•uv add to manage dependencies
•uv run to execute code
•uv sync --frozen in CI/CD
•Commit uv.lock and .python-version

This provides consistent, fast, reproducible Python workflows across all platforms.