Quick Reference
| uv Command | Purpose |
|---|---|
uv init my-project | Create new project |
uv add <package> | Add dependency |
uv add --dev <package> | Add dev dependency |
uv sync | Install all dependencies |
uv run <command> | Run in virtual env |
uv lock --upgrade | Update all deps |
uv python install 3.13 | Install Python version |
| Tool | Command | Speed |
|---|---|---|
| uv | uv add requests | 10-100x faster |
| pip | pip install requests | Baseline |
| ruff Command | Purpose |
|---|---|
ruff check . | Lint code |
ruff check --fix . | Auto-fix issues |
ruff format . | Format code |
| Project Layout | Recommended |
|---|---|
| src layout | src/my_package/ |
| Tests | tests/ |
| Config | pyproject.toml |
When to Use This Skill
Use for project setup and dependencies:
- •Starting new Python projects
- •Setting up uv for fast package management
- •Configuring pyproject.toml
- •Setting up linting with ruff
- •Publishing packages to PyPI
Related skills:
- •For CI/CD: see
python-github-actions - •For testing: see
python-testing - •For type hints config: see
python-type-hints
Python Package Management (2025)
Overview
Modern Python package management centers around uv (the fast Rust-based tool), pip, and pyproject.toml. This guide covers best practices for dependency management, virtual environments, and project configuration.
uv - The Modern Package Manager
Why uv?
- •10-100x faster than pip (written in Rust)
- •Replaces pip, pip-tools, pipx, poetry, pyenv, virtualenv
- •Automatic virtual environment management
- •Lockfile support for reproducibility
- •~200x faster venv creation
Installation
bash
# macOS/Linux curl -LsSf https://astral.sh/uv/install.sh | sh # Windows (PowerShell) irm https://astral.sh/uv/install.ps1 | iex # pip (works everywhere) pip install uv # Homebrew brew install uv
Quick Start
bash
# Create new project uv init my-project cd my-project # Add dependencies uv add requests fastapi pydantic # Add dev dependencies uv add --dev pytest ruff mypy # Sync environment (install all dependencies) uv sync # Run commands in the environment uv run python main.py uv run pytest
Basic Commands
bash
# Package management uv add <package> # Add dependency uv add <package>==1.0.0 # Specific version uv add --dev <package> # Dev dependency uv remove <package> # Remove dependency uv sync # Sync environment with lockfile # Virtual environments uv venv # Create .venv uv venv --python 3.12 # Specific Python version uv venv my-env # Named environment # pip compatibility uv pip install <package> # Install (faster pip) uv pip install -r requirements.txt uv pip freeze > requirements.txt uv pip compile pyproject.toml -o requirements.txt # Python management uv python install 3.13 # Install Python version uv python list # List installed versions uv python pin 3.12 # Pin project Python version # Running uv run <command> # Run in virtual env uv run --with httpx python # Run with temporary package
pyproject.toml with uv
toml
[project]
name = "my-project"
version = "0.1.0"
description = "My Python project"
readme = "README.md"
requires-python = ">=3.11"
license = {text = "MIT"}
authors = [
{name = "Your Name", email = "you@example.com"}
]
dependencies = [
"fastapi>=0.100.0",
"pydantic>=2.0.0",
"httpx>=0.25.0",
]
[project.optional-dependencies]
dev = [
"pytest>=8.0.0",
"ruff>=0.1.0",
"mypy>=1.8.0",
]
[project.scripts]
my-cli = "my_project.cli:main"
[build-system]
requires = ["hatchling"]
build-backend = "hatchling.build"
[tool.uv]
dev-dependencies = [
"pytest>=8.0.0",
"ruff>=0.1.0",
"mypy>=1.8.0",
]
uv.lock
bash
# Lockfile is auto-generated and should be committed # Contains exact versions for reproducibility # Update all dependencies uv lock --upgrade # Update specific package uv lock --upgrade-package requests # Install from lockfile only uv sync --frozen
Project Structure
Recommended: src Layout
code
my-project/ ├── src/ │ └── my_package/ │ ├── __init__.py │ ├── main.py │ ├── models.py │ └── utils/ │ ├── __init__.py │ └── helpers.py ├── tests/ │ ├── __init__.py │ ├── conftest.py │ ├── test_main.py │ └── test_models.py ├── docs/ │ └── index.md ├── pyproject.toml ├── uv.lock ├── README.md ├── LICENSE └── .gitignore
Why src Layout?
- •Prevents import confusion - Can't accidentally import from project root
- •Forces installation - Must install package to test
- •Cleaner distributions - Only package code in wheels
- •Semantic clarity - Clear separation of code, tests, docs
Flat Layout (for simpler projects)
code
my-project/ ├── my_package/ │ ├── __init__.py │ └── main.py ├── tests/ │ └── test_main.py ├── pyproject.toml └── README.md
pyproject.toml Complete Reference
toml
[project]
name = "my-project"
version = "1.0.0"
description = "A comprehensive Python project"
readme = "README.md"
requires-python = ">=3.11"
license = {text = "MIT"}
keywords = ["python", "example", "package"]
classifiers = [
"Development Status :: 4 - Beta",
"Intended Audience :: Developers",
"License :: OSI Approved :: MIT License",
"Programming Language :: Python :: 3",
"Programming Language :: Python :: 3.11",
"Programming Language :: Python :: 3.12",
"Programming Language :: Python :: 3.13",
]
authors = [
{name = "Your Name", email = "you@example.com"}
]
maintainers = [
{name = "Maintainer", email = "maintainer@example.com"}
]
dependencies = [
"fastapi>=0.100.0",
"pydantic>=2.0.0",
"sqlalchemy>=2.0.0",
]
[project.optional-dependencies]
dev = [
"pytest>=8.0.0",
"pytest-cov>=4.0.0",
"ruff>=0.1.0",
"mypy>=1.8.0",
"pre-commit>=3.0.0",
]
docs = [
"mkdocs>=1.5.0",
"mkdocs-material>=9.0.0",
]
all = ["my-project[dev,docs]"]
[project.scripts]
my-cli = "my_package.cli:main"
[project.entry-points."my_package.plugins"]
plugin1 = "my_package.plugins:Plugin1"
[project.urls]
Homepage = "https://github.com/user/my-project"
Documentation = "https://my-project.readthedocs.io"
Repository = "https://github.com/user/my-project"
Changelog = "https://github.com/user/my-project/blob/main/CHANGELOG.md"
[build-system]
requires = ["hatchling"]
build-backend = "hatchling.build"
[tool.hatch.build.targets.wheel]
packages = ["src/my_package"]
# Ruff configuration
[tool.ruff]
target-version = "py311"
line-length = 88
src = ["src", "tests"]
[tool.ruff.lint]
select = [
"E", # pycodestyle errors
"W", # pycodestyle warnings
"F", # Pyflakes
"I", # isort
"B", # flake8-bugbear
"C4", # flake8-comprehensions
"UP", # pyupgrade
"ARG", # flake8-unused-arguments
"SIM", # flake8-simplify
]
ignore = [
"E501", # line too long (handled by formatter)
]
[tool.ruff.lint.isort]
known-first-party = ["my_package"]
[tool.ruff.format]
quote-style = "double"
indent-style = "space"
# Mypy configuration
[tool.mypy]
python_version = "3.12"
strict = true
warn_return_any = true
warn_unused_ignores = true
disallow_untyped_defs = true
plugins = ["pydantic.mypy"]
[[tool.mypy.overrides]]
module = "tests.*"
disallow_untyped_defs = false
# Pytest configuration
[tool.pytest.ini_options]
testpaths = ["tests"]
python_files = ["test_*.py"]
python_functions = ["test_*"]
addopts = [
"-ra",
"-q",
"--strict-markers",
"--cov=src/my_package",
"--cov-report=term-missing",
]
# Coverage configuration
[tool.coverage.run]
branch = true
source = ["src/my_package"]
omit = ["*/tests/*", "*/__init__.py"]
[tool.coverage.report]
exclude_lines = [
"pragma: no cover",
"def __repr__",
"raise NotImplementedError",
"if TYPE_CHECKING:",
]
Ruff - Linting and Formatting
Why Ruff?
- •10-100x faster than Flake8, Black combined
- •Single tool for linting AND formatting
- •800+ built-in rules
- •Auto-fix capabilities
- •Written in Rust (by Astral, same as uv)
Basic Usage
bash
# Linting ruff check . # Check for issues ruff check --fix . # Auto-fix issues ruff check --watch . # Watch mode # Formatting ruff format . # Format all files ruff format --check . # Check formatting # Both ruff check --fix . && ruff format .
Configuration
toml
# pyproject.toml
[tool.ruff]
target-version = "py311"
line-length = 88
src = ["src", "tests"]
[tool.ruff.lint]
select = [
"E", # pycodestyle errors
"W", # pycodestyle warnings
"F", # Pyflakes
"I", # isort
"B", # flake8-bugbear
"C4", # flake8-comprehensions
"UP", # pyupgrade
"ARG", # flake8-unused-arguments
"SIM", # flake8-simplify
"TCH", # flake8-type-checking
"PTH", # flake8-use-pathlib
"ERA", # eradicate (commented code)
"PL", # Pylint
"PERF", # Perflint
"RUF", # Ruff-specific rules
]
ignore = [
"E501", # line too long (handled by formatter)
"PLR0913", # too many arguments
]
# Per-file ignores
[tool.ruff.lint.per-file-ignores]
"tests/**/*.py" = ["S101"] # Allow assert in tests
"__init__.py" = ["F401"] # Allow unused imports
[tool.ruff.lint.isort]
known-first-party = ["my_package"]
force-single-line = true
[tool.ruff.format]
quote-style = "double"
indent-style = "space"
skip-magic-trailing-comma = false
line-ending = "auto"
Pre-commit Integration
yaml
# .pre-commit-config.yaml
repos:
- repo: https://github.com/astral-sh/ruff-pre-commit
rev: v0.4.0
hooks:
- id: ruff
args: [--fix]
- id: ruff-format
- repo: https://github.com/pre-commit/mirrors-mypy
rev: v1.9.0
hooks:
- id: mypy
additional_dependencies:
- pydantic
- types-requests
pip and requirements.txt
When to Use pip
- •Production environments requiring stability
- •Legacy projects
- •Simple scripts without complex dependencies
requirements.txt Best Practices
txt
# requirements.txt - Pinned versions for production fastapi==0.109.0 pydantic==2.5.3 sqlalchemy==2.0.25 httpx==0.26.0 # requirements-dev.txt -r requirements.txt pytest==8.0.0 ruff==0.1.14 mypy==1.8.0
Generating requirements.txt
bash
# From uv uv pip compile pyproject.toml -o requirements.txt uv pip compile pyproject.toml --extra dev -o requirements-dev.txt # From pip-tools pip-compile pyproject.toml -o requirements.txt pip-compile pyproject.toml --extra dev -o requirements-dev.txt # Freeze current environment (not recommended for reproducibility) pip freeze > requirements.txt
Virtual Environment Best Practices
Location
bash
# Recommended: Project-local .venv project/ ├── .venv/ # Virtual environment here ├── src/ ├── tests/ └── pyproject.toml # uv creates .venv by default uv venv # Explicit location uv venv .venv python -m venv .venv
.gitignore
gitignore
# Virtual environments .venv/ venv/ ENV/ env/ # Python __pycache__/ *.py[cod] *$py.class *.so .Python # Distribution build/ dist/ *.egg-info/ # IDE .idea/ .vscode/ *.swp *.swo # Testing .pytest_cache/ .coverage htmlcov/ .mypy_cache/ # Ruff .ruff_cache/
Activation (when needed)
bash
# Usually not needed with uv - just use `uv run` # Linux/macOS source .venv/bin/activate # Windows (PowerShell) .venv\Scripts\Activate.ps1 # Windows (cmd) .venv\Scripts\activate.bat # Deactivate deactivate
Publishing Packages
Build and Publish
bash
# Build with uv uv build # Publish to PyPI uv publish # Or with twine pip install twine twine upload dist/* # Test PyPI first twine upload --repository testpypi dist/*
Version Management
toml
# pyproject.toml - dynamic version from __init__.py [project] dynamic = ["version"] [tool.hatch.version] path = "src/my_package/__init__.py"
python
# src/my_package/__init__.py __version__ = "1.0.0"