migrate-to-uv

Migrate to uv

Convert Python projects from Poetry/pipx/pip to uv.

Pre-Migration Assessment

IMPORTANT: Before starting any migration, assess the project for blockers. Read pyproject.toml, setup.py (if present), and the build configuration to check for the following. Report findings to the user before proceeding.

Check 1: C/C++/Rust Extensions

Look for signs of compiled extensions:

• setup.py with ext_modules, cffi, cython, or Extension() calls
• Build dependencies like setuptools, cffi, cython, pybind11, maturin, scikit-build-core
• .c, .cpp, .pyx, or .rs source files referenced in the build

If found: uv_build does NOT support compiling C/C++/Rust extensions. The project must use a compatible build backend (setuptools, scikit-build-core, maturin, or hatchling with extension plugins). This is a non-trivial change — warn the user that the build backend swap may require significant effort and testing, especially for projects with complex setup.py logic.

Check 2: Private Package Indexes

Look for [[tool.poetry.source]] sections or references to private PyPI mirrors.

If found: uv handles authentication differently from Poetry. Poetry uses poetry config http-basic.<name> <user> <pass>, while uv uses environment variables:

• UV_INDEX_<NAME>_USERNAME / UV_INDEX_<NAME>_PASSWORD
• Or UV_INDEX_URL with credentials embedded
• Or keyring integration

The migration tool won't convert auth config. The user needs to set up credentials separately for CI and local dev. See the "Private indexes" section below for format conversion.

Check 3: Monorepo / Multiple pyproject.toml Files

Look for multiple pyproject.toml files, path dependencies between packages, or Poetry monorepo plugins (poetry-plugin-monorepo, monoranger).

If found: This is actually a good candidate for migration — uv workspaces handle monorepos much better than Poetry. But the migration is more involved than a single-package project. See the "Monorepo / Workspace Migration" section below.

Check 4: Tox Configuration

Look for tox.ini or [tool.tox] sections.

If found: tox creates its own virtualenvs using pip by default. While tox can be configured to use uv, consider whether uv run --python 3.X pytest can replace tox environments entirely. This is a separate concern from the Poetry migration — tox can coexist with uv.

Quick Start: Automated Migration

For most Poetry projects, use the migrate-to-uv tool:

uvx migrate-to-uv

What it does:

• Parses [tool.poetry] sections and converts to PEP 621 [project] format
• Converts Poetry version specifiers (^, ~) to PEP 440 format (>=, <)
• Moves [tool.poetry.group.*.dependencies] to [dependency-groups]
• Converts [tool.poetry.scripts] to [project.scripts]
• Converts [tool.poetry.extras] to [project.optional-dependencies]
• Handles git/path/url dependencies → [tool.uv.sources]
• Preserves exact versions from poetry.lock when generating uv.lock
• Deletes poetry.lock after successful conversion

After running, verify and test:

rm -rf .venv
uv sync
uv run pytest

Note: The tool does NOT change the build backend. You may need to manually update [build-system] from poetry-core to hatchling (see step 6 below).

Manual Migration Steps

Use manual migration for complex projects or when automated tool fails.

1. Convert Metadata

Poetry → PEP 621:

# BEFORE: [tool.poetry]
[tool.poetry]
name = "myapp"
version = "1.0.0"
description = "My app"
authors = ["John Doe <john@example.com>"]
license = "MIT"
readme = "README.md"

# AFTER: [project]
[project]
name = "myapp"
version = "1.0.0"
description = "My app"
authors = [{name = "John Doe", email = "john@example.com"}]
license = {text = "MIT"}
readme = "README.md"

2. Convert Dependencies

Version specifier conversions:

• ^1.2.3 → >=1.2.3,<2.0.0 (caret = compatible)
• ~1.2.3 → >=1.2.3,<1.3.0 (tilde = patch only)
• python = "^3.10" → requires-python = ">=3.10,<4.0"

# BEFORE
[tool.poetry.dependencies]
python = "^3.10"
requests = "^2.26.0"
pandas = {version = "^2.0", extras = ["excel"]}

# AFTER
[project]
requires-python = ">=3.10,<4.0"
dependencies = [
    "requests>=2.26.0,<3.0.0",
    "pandas[excel]>=2.0,<3.0",
]

3. Convert Dev Dependencies

Poetry groups → [dependency-groups] (PEP 735):

# BEFORE
[tool.poetry.group.dev.dependencies]
pytest = "^7.0"
ruff = "^0.1.0"

[tool.poetry.group.docs.dependencies]
sphinx = "^7.0"

# AFTER
[dependency-groups]
dev = [
    "pytest>=7.0,<8.0",
    "ruff>=0.1.0,<1.0",
]
docs = ["sphinx>=7.0,<8.0"]

4. Convert Scripts

# BEFORE
[tool.poetry.scripts]
myapp = "myapp.cli:main"

# AFTER
[project.scripts]
myapp = "myapp.cli:main"

5. Convert Extras (Optional Dependencies)

# BEFORE
[tool.poetry.dependencies]
psycopg2 = {version = "^2.9", optional = true}

[tool.poetry.extras]
postgresql = ["psycopg2"]

# AFTER
[project.optional-dependencies]
postgresql = ["psycopg2>=2.9,<3.0"]

6. Set Build Backend

Choose based on project type:

# Option 1: hatchling (recommended for most projects)
[build-system]
requires = ["hatchling"]
build-backend = "hatchling.build"

[tool.hatch.build.targets.wheel]
packages = ["src/myapp"]  # if using src layout

# Option 2: uv_build (fastest, pure Python only — NO C/C++/Rust extensions)
[build-system]
requires = ["uv_build>=0.6,<0.7"]
build-backend = "uv_build"

[tool.uv.build-backend]
module-name = "myapp"     # use a plain string, NOT a list — list syntax breaks on older uv
module-root = ""          # "" for flat layout, "src" for src layout

# Option 3: setuptools (required for C extensions with ext_modules)
[build-system]
requires = ["setuptools>=61", "cffi"]  # add extension build deps
build-backend = "setuptools.build_meta"

# Option 4: scikit-build-core (for CMake-based C++ extensions)
[build-system]
requires = ["scikit-build-core"]
build-backend = "scikit_build_core.build"

# Option 5: maturin (for Rust extensions via PyO3)
[build-system]
requires = ["maturin>=1.0,<2.0"]
build-backend = "maturin"

WARNING: uv_build does NOT support compiling C/C++/Rust extensions. If the project has compiled extensions, you MUST use setuptools, scikit-build-core, or maturin as the build backend.

Do NOT use setuptools with license = {text = "MIT"} — it has a known bug. Use license = "MIT" string form instead when using setuptools.

7. Convert Special Dependencies

Git dependencies:

# BEFORE
[tool.poetry.dependencies]
httpx = {git = "https://github.com/encode/httpx.git", tag = "0.27.0"}

# AFTER
[project]
dependencies = ["httpx"]

[tool.uv.sources]
httpx = {git = "https://github.com/encode/httpx", tag = "0.27.0"}

Path dependencies:

# BEFORE
[tool.poetry.dependencies]
mylib = {path = "../mylib", develop = true}

# AFTER
[project]
dependencies = ["mylib"]

[tool.uv.sources]
mylib = {path = "../mylib", editable = true}

Private indexes:

# BEFORE
[[tool.poetry.source]]
name = "private"
url = "https://pypi.company.com/simple"

# AFTER
[[tool.uv.index]]
name = "private"
url = "https://pypi.company.com/simple"

Private index authentication (Poetry uses poetry config http-basic, uv uses env vars):

# Option 1: Environment variables (recommended for CI)
export UV_INDEX_PRIVATE_USERNAME="user"
export UV_INDEX_PRIVATE_PASSWORD="token"

# Option 2: Credentials in URL (use with caution)
# [[tool.uv.index]]
# url = "https://user:token@pypi.company.com/simple"

# Option 3: keyring integration
uv --keyring-provider subprocess ...

8. Add uv Configuration

[tool.uv]
package = true  # if this is an installable package

9. Generate Lock and Test

rm poetry.lock
rm -rf .venv
uv lock
uv sync --all-extras --dev
uv run pytest

Monorepo / Workspace Migration

If the project has multiple packages with Poetry path dependencies, convert to a uv workspace.

1. Create workspace root

Add a pyproject.toml at the repository root (or use an existing one):

[project]
name = "my-monorepo"
version = "0.0.0"
requires-python = ">=3.10"

[tool.uv.workspace]
members = ["packages/*", "services/*"]

[tool.uv]
package = false  # the root is not an installable package

2. Convert each member package

Run the migration (automated or manual) for each pyproject.toml individually. Convert Poetry path dependencies to uv sources:

# BEFORE (in services/service-a/pyproject.toml)
[tool.poetry.dependencies]
lib-core = {path = "../../packages/lib-core", develop = true}

# AFTER
[project]
dependencies = ["lib-core"]

[tool.uv.sources]
lib-core = {workspace = true}

3. Generate unified lockfile

# Remove per-package Poetry lockfiles
find . -name "poetry.lock" -delete
rm -rf .venv

# Generate single workspace lockfile at the root
uv lock
uv sync --all-packages

Key differences from Poetry monorepos:

• Single uv.lock at workspace root instead of per-package lockfiles
• uv sync installs all workspace members in one environment
• Cross-package dependencies use {workspace = true} instead of relative paths
• No need for monorepo plugins (poetry-plugin-monorepo, monoranger)

Converting pipx to uv tool

Replace pipx installations with uv:

# BEFORE
pipx install black
pipx install ruff

# AFTER
uv tool install black
uv tool install ruff

# For editable local installs (git pull updates automatically)
uv tool install -e .

Converting requirements.txt

# Generate pyproject.toml from requirements.txt
uv init
uv add $(cat requirements.txt | grep -v '^#' | grep -v '^$' | tr '\n' ' ')

# Or keep requirements.txt and use uv pip
uv pip install -r requirements.txt

Command Equivalents

Poetry	uv
poetry install	uv sync
poetry install --with dev	uv sync --dev
poetry add requests	uv add requests
poetry add pytest --group dev	uv add pytest --dev
poetry remove requests	uv remove requests
poetry run pytest	uv run pytest
poetry build	uv build
poetry publish	uv publish
poetry lock	uv lock
poetry update	uv lock --upgrade

pipx	uv
pipx install pkg	uv tool install pkg
pipx run pkg	uvx pkg
pipx list	uv tool list
pipx upgrade pkg	uv tool upgrade pkg
pipx uninstall pkg	uv tool uninstall pkg

CI/CD Updates

GitHub Actions:

# BEFORE
- run: pip install poetry
- run: poetry install

# AFTER
- uses: astral-sh/setup-uv@v5
- run: uv sync --frozen

Docker:

# BEFORE
RUN pip install poetry && poetry install --no-root

# AFTER
COPY --from=ghcr.io/astral-sh/uv:latest /uv /bin/uv
RUN --mount=type=cache,target=/root/.cache/uv uv sync --frozen

README Updates

Update installation instructions:

## Installation

Clone the repository, then:

\`\`\`bash
uv tool install -e .
\`\`\`

Updates are automatic after `git pull`.

Cleanup Checklist

After migration:

• Delete poetry.lock
• Delete old .venv
• Remove [tool.poetry] sections from pyproject.toml
• Remove [build-system] with poetry-core
• Update README installation instructions
• Update CI/CD pipelines
• Update Dockerfile if applicable
• Run full test suite
• Commit changes