UV (pronounced “ultraviolet”) is an extremely fast Python package installer and resolver, designed to be a drop-in replacement for pip/pip-tools with significant performance improvements. This guide covers everything you need to know about using UV in your Python projects.

If you’re looking for a simplified explanation of the UV package manager, check out this helpful guide: UV Package Manager — A Simplified Guide

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The Ultimate Guide to UV Package Manager

Table of Contents

· Table of Contents
· Installation
· Project Initialization
· Project Structure
· Initialization Options
· Package Management
· Adding Packages
· Removing Packages
· Dependency Resolution
· Dependency Tree
· Virtual Environment Management
· Syncing Dependencies
· Running Scripts
· Working with pip
· UV Pip Commands
· Converting pip Projects
· Tool Management
· Installing Tools
· Running Tools
· Managing Tools
· UV Shortcuts
· Advanced Usage
· Configuration
· CI/CD Integration
· Performance Comparisons
· Troubleshooting
· Issue: Package not found
· Issue: Permission errors
· Issue: Lock file conflicts
· Issue: Network problems
· FAQs

Installation

To install UV globally on your system:

# Using pip
pip install uv

# Using pipx (recommended for CLI tools)
pipx install uv# Using homebrew (macOS)
brew install uv

Project Initialization

Initialize a new Python project with UV:

uv init my_newapp

Project Structure

When you initialize a new project with uv init, the following folder structure is created:

my_newapp/
├── .git/                    # Git repository
├── .gitignore               # Common Python gitignore patterns
├── .python-version          # Python version specification
├── README.md                # Basic README file
├── main.py                  # Main Python entry point
└── pyproject.toml           # Project configuration

Let’s look at the default content of some of these files:

pyproject.toml

[project]
name = "my_newapp"
version = "0.1.0"
description = "Add your description here"
dependencies = []
readme = "README.md"
requires-python = ">= 3.8"

[build-system]
requires = ["hatchling"]
build-backend = "hatchling.build"

[tool.rye]
managed = true
dev-dependencies = []

main.py

def main():
    print("Hello, world!")

if __name__ == "__main__":
    main()

.gitignore

__pycache__/
*.py[cod]
*$py.class
*.so
.Python
env/
build/
develop-eggs/
dist/
downloads/
eggs/
.eggs/
lib/
lib64/
parts/
sdist/
var/
wheels/
*.egg-info/
.installed.cfg
*.egg
.env
.venv
.uv

Initialization Options

UV offers various options when initializing a project:

# Initialize in existing directory
cd existing_directory
uv init --app

# Initialize as a distributable Python library
uv init my_library --lib

# Initialize with specific Python version
uv init my_project --python=3.11

# Initialize with git disabled
uv init my_project --no-git

After initialization, you can check the project structure:

# List all files including hidden ones
ls -la my_newapp

# View directory tree
find my_newapp -type f | sort

Package Management

Adding Packages

Add packages to your project:

# Add one or more packages
uv add flask requests

# Add a specific version
uv add "requests>=2.28.0"

# Add packages with extras
uv add "celery[redis]"

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

# Add from requirements file
uv add -r requirements.txt

When you add packages, UV updates both the pyproject.toml and creates a uv.lock file:

Updated pyproject.toml after adding Flask and requests

[project]
name = "my_newapp"
version = "0.1.0"
description = "Add your description here"
dependencies = [
    "flask>=2.3.3",
    "requests>=2.31.0",
]
readme = "README.md"
requires-python = ">= 3.8"

[build-system]
requires = ["hatchling"]
build-backend = "hatchling.build"

[tool.rye]
managed = true
dev-dependencies = []

The uv.lock file will contain exact versions and hashes for all dependencies and sub-dependencies. This ensures reproducible builds across different environments.

Removing Packages

Remove packages from your project:

# Remove a single package
uv remove flask

# Remove multiple packages
uv remove flask requests

# Remove a development dependency
uv remove --dev pytest

Dependency Resolution

UV has an extremely fast dependency resolver. When conflicts arise, it provides clear error messages:

Error: Failed to resolve dependencies
  • flask==2.0.0 requires werkzeug>=2.0.0, but werkzeug==1.0.1 is installed.
  • flask-admin==1.5.8 requires werkzeug<2.0,>=0.15, which conflicts with flask==2.0.0.

Dependency Tree

View the dependency tree of your project:

uv tree

Example output:

flask 2.3.3
├── blinker>=1.6.2 1.6.3
├── click>=8.1.3 8.1.7
├── itsdangerous>=2.1.2 2.1.2
├── jinja2>=3.1.2 3.1.2
│   └── markupsafe>=2.0 2.1.3
└── werkzeug>=2.3.7 2.3.7

requests 2.31.0
├── certifi>=2017.4.17 2023.7.22
├── charset-normalizer<4,>=2 3.2.0
├── idna<4,>=2.5 3.4
└── urllib3<3,>=1.21.1 2.0.4

Virtual Environment Management

Syncing Dependencies

UV automatically creates and manages virtual environments. To ensure all project dependencies match the locked versions:

# Create/update virtual environment from lock file
uv sync

# Force reinstallation of all packages
uv sync --reinstall

# Update all dependencies to latest versions
uv sync --upgrade

Check the created virtual environment structure:

.uv/
├── env/                    # Virtual environment directory
│   ├── bin/                # Executables
│   ├── include/            # C headers
│   ├── lib/                # Python packages
│   └── pyvenv.cfg          # Environment configuration
└── store/                  # Package cache

Running Scripts

Run Python scripts with the project’s dependencies:

# Run a script using the project's environment
uv run main.py

# Run with arguments
uv run main.py --arg1 value1

# Run a module
uv run -m pytest

# Run an expression
uv run -c "import flask; print(flask.__version__)"

# Run with environment variables
UV_CONFIG_FILE=custom_config.toml uv run main.py

Check which Python interpreter is being used:

uv run -c "import sys; print(sys.executable)"

Example output:

/Users/username/projects/my_newapp/.uv/env/bin/python

Working with pip

UV Pip Commands

UV provides compatibility with pip commands:

# Install packages with pip syntax
uv pip install numpy pandas matplotlib

# Install from requirements.txt
uv pip install -r requirements.txt

# Install in development mode
uv pip install -e .

# List installed packages
uv pip list

# Show package details
uv pip show requests

# Create requirements.txt file
uv pip freeze > requirements.txt

# Verify installed packages
uv pip check

Example uv pip list output:

Package         Version
--------------- -------
click           8.1.7
flask           2.3.3
itsdangerous    2.1.2
jinja2          3.1.2
markupsafe      2.1.3
pip             23.2.1
requests        2.31.0
setuptools      68.2.2
werkzeug        2.3.7
wheel           0.41.2

Converting pip Projects

Convert existing pip-based projects to UV:

# Step 1: Initialize the project structure
uv init --app

# Step 2: Add requirements from requirements.txt
uv add -r requirements.txt

# Optional: Add dev dependencies
uv add --dev -r dev-requirements.txt

Tool Management

UV provides isolated tool installation and execution, similar to pipx.

Installing Tools

# Install a tool in an isolated environment
uv tool install ruff

# Install multiple tools
uv tool install black mypy isort

# Install a specific version
uv tool install "black==23.7.0"

# Find the installation path
which ruff
# Output: ~/.uv/tools/bin/ruff

The tools directory structure looks like:

~/.uv/
└── tools/
    ├── bin/            # Executable symlinks
    └── environments/   # Isolated environments for each tool
        ├── black/
        ├── ruff/
        └── mypy/

Running Tools

# Run an installed tool
ruff check .

# Run a tool without installing it (temporary environment)
uv tool run ruff check .

# Run with specific version
uv tool run "ruff==0.0.292" check .

# Run with arguments
uv tool run black --check --diff .

Managing Tools

# List installed tools
uv tool list

# Upgrade a specific tool
uv tool upgrade ruff

# Upgrade all tools
uv tool upgrade --all

# Uninstall a tool
uv tool uninstall ruff

Example uv tool list output:

Package    Version Location
---------- ------- ---------------------------------
black      23.9.1  ~/.uv/tools/environments/black
mypy       1.5.1   ~/.uv/tools/environments/mypy
ruff       0.0.292 ~/.uv/tools/environments/ruff

UV Shortcuts

UV provides shortcuts for common operations:

# Shortcut for 'uv tool run'
uvx ruff check .

# Additional examples
uvx black .
uvx mypy main.py
uvx isort --check .

Advanced Usage

Configuration

UV can be configured through environment variables or a configuration file.

Environment Variables:

# Set cache directory
export UV_CACHE_DIR=~/.cache/uv

# Set Python version
export UV_PYTHON=python3.11

# Disable network access (for CI/CD)
export UV_NO_NETWORK=1

Configuration File (~/.config/uv/config.toml):

[uv]
cache_dir = "~/.cache/uv"
python = "python3.11"
no_network = false
index_url = "https://pypi.org/simple"

CI/CD Integration

UV works well in CI/CD pipelines with fast, reproducible installations:

.github/workflows/ci.yml

name: CI

on: [push, pull_request]

jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3
      - name: Set up Python
        uses: actions/setup-python@v4
        with:
          python-version: '3.11'
      - name: Install UV
        run: pip install uv
      - name: Install dependencies
        run: uv sync
      - name: Run tests
        run: uv run -m pytest

Performance Comparisons

UV is significantly faster than traditional Python package managers:

Operation pip pip-tools poetry UV Install Django 8.2s 7.6s 6.3s 1.2s Resolve deps 15.3s 12.1s 10.5s 0.8s Cold cache 25.1s 22.3s 19.8s 3.5s

Troubleshooting

Common issues and solutions:

Issue: Package not found

Error: Could not find a version that satisfies the requirement 'non-existent-package'

Solution: Check the spelling and verify the package exists on PyPI.

Issue: Permission errors

Error: Permission denied when accessing directory '/usr/local/lib/python3.11/site-packages'

Solution: Use --user flag or set up a virtual environment.

Issue: Lock file conflicts

Error: Lock file is out of date with pyproject.toml

Solution: Run uv sync --update to update the lock file.

Issue: Network problems

Error: Could not fetch URL https://pypi.org/simple/requests/: connection failed

Solution: Check internet connection or configure a different package index.

FAQs

Q: How does UV compare to Poetry? A: UV is primarily focused on being a fast pip replacement, while Poetry is a more comprehensive dependency management and packaging tool. UV can be 5–10x faster than Poetry for installation operations.

Q: Can I use UV with existing requirements.txt files? A: Yes, use uv pip install -r requirements.txt or convert to UV format with uv add -r requirements.txt.

Q: Does UV support private package repositories? A: Yes, UV supports custom package indexes through environment variables or configuration files.

Q: Is UV compatible with all Python versions? A: UV supports Python 3.8 and newer.

Q: How does UV handle conflicting dependencies? A: UV uses an advanced dependency resolver that provides clear error messages about conflicts.

UV simplifies Python project management with lightning-fast performance while maintaining compatibility with existing Python packaging standards. Its integrated tooling for environment management, dependency resolution, and tool execution makes it an excellent choice for both new and existing projects.

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UV Package Manager: The Comprehensive Guide

UV Package Manager: A Simplified Guide