uv Project Layout and Dependency Management

!!! info "Primary sources" - uv project guide - uv project layout - uv Docker integration

Core Files

File	Purpose	Commit?
`pyproject.toml`	Project metadata, deps, tool config	Yes
`uv.lock`	Exact resolved versions, cross-platform	Yes
`.python-version`	Default Python version for the project	Yes
`.venv/`	Local virtual environment	No (`.gitignore`)

!!! warning "Commit the lockfile" uv.lock must be committed. It is the source of truth for reproducible installs in CI and Docker. Never edit it by hand.

Essential Commands

# Initialize a new project (app, not library)
uv init --app

# Initialize a library (installable package with src layout)
uv init --lib

# Add a runtime dependency
uv add fastapi[standard]

# Add multiple dependencies at once
uv add uvicorn[standard] pydantic-settings

# Add dev-only dependency
uv add --dev pytest httpx pytest-asyncio ruff mypy

# Remove a dependency
uv remove requests

# Upgrade a specific package (keeps rest of lockfile intact)
uv lock --upgrade-package fastapi

# Upgrade all packages
uv lock --upgrade

# Sync env to lockfile (install/remove as needed)
uv sync

# Sync without dev deps (e.g., in CI or Docker)
uv sync --no-dev

# Sync and assert lockfile is up-to-date (for CI / Docker)
uv sync --locked

# Run a command in the project environment
uv run pytest
uv run uvicorn my_app.main:app --reload

# Run a one-off command without installing anything permanently
uv run --with httpx python -c "import httpx; print(httpx.__version__)"

pyproject.toml Reference

[project]
name = "my-app"
version = "0.1.0"
description = "Production FastAPI service"
requires-python = ">=3.12"
license = { text = "MIT" }
readme = "README.md"

dependencies = [
    "fastapi[standard]>=0.115",
    "uvicorn[standard]>=0.34",
    "pydantic-settings>=2.0",
]

[project.scripts]
# Creates `my-app` CLI entry point when installed
my-app = "my_app.main:main"

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

[tool.hatch.build.targets.wheel]
packages = ["src/my_app"]

[tool.uv]
dev-dependencies = [
    "pytest>=8",
    "pytest-asyncio>=0.24",
    "httpx>=0.27",     # needed for FastAPI TestClient
    "ruff>=0.6",
    "mypy>=1.11",
]

[tool.pytest.ini_options]
testpaths = ["tests"]
asyncio_mode = "auto"
strict-markers = true

[tool.ruff.lint]
select = ["E", "F", "I", "UP", "B", "S"]

[tool.mypy]
strict = true

src Layout with uv

Use uv init --lib or set up manually:

my-app/
├── pyproject.toml
├── uv.lock
├── .python-version    # e.g., "3.12"
├── .env.example
├── README.md
├── src/
│   └── my_app/
│       └── __init__.py
└── tests/
    └── conftest.py

The src/ layout prevents the local directory from shadowing the installed package, which would otherwise cause silent test failures when testing the installed version.

hatchling config for src layout:

[tool.hatch.build.targets.wheel]
packages = ["src/my_app"]

Migration from pip / requirements.txt

# 1. Initialize uv in an existing project
uv init --no-workspace   # if already has pyproject.toml, skip this

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

# 3. Import dev requirements
uv add --dev -r requirements-dev.txt

# 4. Verify lockfile was created
cat uv.lock | head -20

# 5. Clean up old files
rm requirements.txt requirements-dev.txt setup.py setup.cfg Pipfile Pipfile.lock

# 6. Add .venv to .gitignore
echo ".venv/" >> .gitignore

uv in Docker

The canonical pattern uses --mount=type=cache for fast rebuilds and --no-install-project for layer separation:

# Copy uv binary (pin the version)
COPY --from=ghcr.io/astral-sh/uv:0.5.27 /uv /uvx /bin/

WORKDIR /app

# Layer 1: install dependencies (changes rarely → cached aggressively)
RUN --mount=type=cache,target=/root/.cache/uv \
    --mount=type=bind,source=uv.lock,target=uv.lock \
    --mount=type=bind,source=pyproject.toml,target=pyproject.toml \
    uv sync --locked --no-install-project --no-editable

# Layer 2: copy source and install project (changes frequently)
COPY . /app
RUN --mount=type=cache,target=/root/.cache/uv \
    uv sync --locked --no-editable

Key flags:

Flag	Effect
`--locked`	Fail if `uv.lock` is out of date with `pyproject.toml`
`--no-install-project`	Install deps but not the project itself (layer separation)
`--no-editable`	Install in non-editable mode (copy code into `.venv`, not symlink)
`--no-dev`	Skip dev dependencies (use in production images)
`--compile-bytecode`	Pre-compile `.pyc` files (faster startup, larger image)

After syncing, activate the venv via PATH (not uv run) in production:

ENV PATH="/app/.venv/bin:$PATH"
CMD ["uvicorn", "my_app.main:app", "--host", "0.0.0.0", "--port", "8000"]

Using CMD ["uv", "run", "uvicorn", ...] in production is fine but adds a small overhead and requires uv to be present in the final image.

CI/CD with uv

# GitHub Actions example
- name: Install uv
  uses: astral-sh/setup-uv@v4
  with:
    version: "0.5.27"   # pin for reproducibility

- name: Sync dependencies
  run: uv sync --locked

- name: Run tests
  run: uv run pytest --tb=short

- name: Lint
  run: uv run ruff check .

- name: Type check
  run: uv run mypy src/

.gitignore Entries for uv Projects

.venv/
__pycache__/
*.pyc
.env
dist/
*.egg-info/
.mypy_cache/
.ruff_cache/
.pytest_cache/

Do NOT ignore uv.lock — it must be committed.

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