Python Project

UV Project Management

Guide for managing Python projects using the uv package manager with proper understanding of modern Python project structures.

Key Concepts

Fetch Versions of a package

For newly added dependency or when need to upgrade the version of a dependency, use pip to fetch versions.

Use uv pip index versions <package> to fetch versions

Dependency Groups vs Optional Dependencies

Modern Python projects using uv should use dependency-groups instead of [project.optional-dependencies]:

Use [dependency-groups] (PEP 735):

[dependency-groups]
dev = [
    "pytest>=9.0.0",
    "ruff>=0.14.0",
]
test = [
    "pytest>=9.0.0",
    "pytest-cov>=4.0.0",
]

Avoid [project.optional-dependencies]:

# ❌ Old pattern - don't use with uv
[project.optional-dependencies]
dev = ["pytest>=9.0.0"]

Installing Dependency Groups

Install specific dependency groups:

uv sync --group dev
uv sync --group test

Install all groups:

uv sync --all-groups

Install without any groups:

uv sync --no-dev

Common Patterns

Basic pyproject.toml Structure

[project]
name = "my-project"
version = "0.1.0"
description = "Project description"
requires-python = ">=3.11"
dependencies = [
    "requests>=2.31.0",
    "pydantic>=2.0.0",
]

[dependency-groups]
dev = [
    "pytest>=9.0.0",
    "ruff>=0.14.0",
    "mypy>=1.8.0",
]

[build-system]
requires = ["setuptools", "wheel"]
build-backend = "setuptools.build_meta"

Project Initialization

Create new project:

uv init my-project
cd my-project

Add dependencies:

# Production dependency
uv add requests

# Dev dependency
uv add --group dev pytest

Running Commands

Run Python with project dependencies:

uv run python script.py
uv run pytest

Run installed tools:

uv run ruff check .
uv run mypy src/

Syncing Dependencies

Sync all dependencies and groups:

uv sync --all-groups

Lock dependencies without installing:

uv lock

Migration from Old Patterns

When updating projects from optional-dependencies to dependency-groups:

1. Rename section:

   # Change from:
   [project.optional-dependencies]
   # To:
   [dependency-groups]
   

2. Update installation commands:

   # Change from:
   pip install -e ".[dev]"
   # To:
   uv sync --group dev
   

3. Update CI/CD scripts to use uv sync --all-groups or specific groups

Pytest

use pytest for testing. place tests under ./tests/. And never create './tests/init.py`

Also follow the no __init__.py convention of pytest, that's no __init__.py in all subdirectories in ./tests.

If anything shall be shared, use conftest.py.

options in pyproject.toml:

[tool.pytest]
addopts = ["--import-mode=importlib"]
pythonpath = ["src"]
testpaths = ["tests"]

Do NOTE that don't create folders in tests that are the same name with your bebing tested package.

So this file structure is NOT allowed cause it will shadow your package.

src/app/__init__.py
src/app/mymodule.py
tests/app/__init__.py
tests/app/test_mymodule.py # this will shadow and fail to import app.mymodule

pytest fixtures

fixtures are shared test objects among all tests.

use @pytest.fixture def some_fixture() to create a fixture.

declare tests with args of the same name to request the fixture. def test

@pytest.fixture
def sample_data1():
    reutrn "a"

@pytest.fixture
def sample_data(sample_data1):
    """fixture can also request another fixture"""
    return f"hello {sample_data1)"

def test_ok(sample_data):
    assert "hello a" == sample_data

test asset files with fixture

use tests/conftest.py to manage shared fixtures, and also it's a common pattern to provide file paths in conftest.py as fixtures.

The rational is you have stable file path handling if you do all the relative paths in a single conftest.py file.

import pytest
from pathlib import Path

@pytest.fixture
def test_data_dir():
    """Returns the absolute path to the directory containing test assets."""
    return Path(__file__).parent / "data"

@pytest.fixture
def sample_json(test_data_dir):
    """Provides the path to a specific asset."""
    return test_data_dir / "sample_input.json"

Best Practices

1. Always use dependency-groups for dev/test/docs dependencies with uv
2. Pin major versions in dependencies: package>=1.0.0,<2.0.0
3. Use uv.lock for reproducible environments (committed to git)
4. Run via uv run to ensure correct environment: uv run pytest not pytest
5. Group related dependencies: separate dev, test, docs, lint groups as needed

Common Commands Reference

# Project setup
uv init              # Initialize new project
uv sync              # Install dependencies from pyproject.toml
uv sync --all-groups # Install with all dependency groups

# Dependency management
uv add package       # Add production dependency
uv add --group dev package  # Add to dependency group
uv remove package    # Remove dependency
uv lock              # Update uv.lock file

# Running code
uv run python script.py    # Run Python with project deps
uv run pytest             # Run tests
uv run --with package cmd # One-off dependency

# Environment info
uv pip list          # List installed packages
uv pip show package  # Show package details

Troubleshooting

Issue: Old pip install -e ".[dev]" pattern doesn't work

• Solution: Use uv sync --group dev instead

Issue: Dependencies not found when running scripts

• Solution: Use uv run python script.py instead of python script.py

Issue: Need to add dependency to specific group

• Solution: uv add --group dev package-name