Py Modernize

Python Codebase Modernization

Upgrade Python projects to use modern tooling, syntax, and patterns following Engineering Charter principles.

Objectives

1. Migrate from pip to uv for faster dependency management
2. Upgrade Python syntax to 3.13+ modern patterns
3. Replace deprecated APIs and patterns
4. Update tooling to current best practices
5. Ensure pyproject.toml is the single source of configuration

Required Tools

Install uv globally (via package manager): sudo zypper install uv or pip install --user uv Add to [dependency-groups] dev: "pyupgrade", "ruff"

• uv: Fast package installer (pip replacement)
• pyupgrade: Auto-upgrade syntax to newer Python
• ruff: Modern linter with UP rules

Permissions: Run py-quality-setup first to configure .claude/settings.local.json with all needed tool permissions.

Package Manager: pip → uv

Why uv?

• 10-100x faster than pip
• Better dependency resolution
• Improved caching
• Compatible with pip (drop-in replacement)
• Actively developed by Astral (same team as ruff)

Migration Workflow

# 1. Verify current setup
cat requirements.txt setup.py setup.cfg pyproject.toml

# 2. Install uv globally (not recommended, ask user to install via package manager)
# curl -LsSf https://astral.sh/uv/install.sh | sh

# 3. Replace venv creation
# OLD: python -m venv venv
uv venv

# 4. Replace pip install
# OLD: pip install -e ".[dev]"
uv pip install -e ".[dev]"

# 5. Replace pip install from requirements.txt
# OLD: pip install -r requirements.txt
uv pip install -r requirements.txt

# 6. Compile requirements (faster dependency resolution)
uv pip compile pyproject.toml -o requirements.txt

# 7. Sync environment (install exactly what's in requirements.txt)
uv pip sync requirements.txt

Update CI/CD

# .github/workflows/test.yml

# BEFORE
- name: Install dependencies
  run: |
    python -m venv venv
    source venv/bin/activate
    pip install -e ".[dev]"

# AFTER
- name: Install uv
  uses: astral-sh/setup-uv@v1

- name: Install dependencies
  run: |
    uv venv
    source .venv/bin/activate
    uv pip install -e ".[dev]"

Update Documentation

Update README.md:

## Development Setup

python -m venv venv
source venv/bin/activate
pip install -e ".[dev]"

## Development Setup

# Install uv if not already installed (via package manager preferred)
# sudo zypper install uv  # openSUSE
# or: pip install --user uv

uv venv
source .venv/bin/activate
uv pip install -e ".[dev]"

Python Syntax Modernization

Target Version

Set target in pyproject.toml:

[project]
requires-python = ">=3.13"

[tool.pyupgrade]
target-version = "py313"

[tool.ruff]
target-version = "py313"

[tool.ruff.lint]
select = ["UP"]  # Enable pyupgrade rules

Run Syntax Upgrades

# Using pyupgrade directly (modifies files in-place)
pyupgrade --py313-plus **/*.py

# Using ruff (shows what would change)
ruff check . --select UP
ruff check . --select UP --fix  # Apply fixes

# Verify changes
git diff

# Run tests to ensure functionality preserved
pytest

Common Modernizations

Run pyupgrade --py313-plus . or ruff check . --select UP to auto-upgrade:

• Type hints: List[str] → list[str], Optional[int] → int | None
• Remove __future__: imports (built-in 3.11+)
• String formatting: % or .format() → f-strings
• Type unions: Union[int, str] → int | str
• Walrus operator: if x := func(): (reduce temp variables)
• Match statements: Replace long if/elif chains (3.10+)
• Pathlib: Replace os.path with Path objects
• Dataclasses: Replace manual __init__ with @dataclass

Configuration Modernization

Consolidate setup.py/setup.cfg/requirements.txt → pyproject.toml.

Note: For complete pyproject.toml configuration including ruff, mypy, and basedpyright, see py-quality-setup.

Basic structure:

[project]
name = "myproject"
version = "1.0.0"
requires-python = ">=3.13"
dependencies = ["requests", "pydantic"]

[build-system]
requires = ["setuptools>=68.0"]
build-backend = "setuptools.build_meta"

After: rm setup.py setup.cfg; uv pip install -e .; pytest

Deprecated Pattern Updates

Common deprecations to fix:

• collections.Iterable → collections.abc.Iterable (deprecated 3.3, removed 3.10)
• datetime.utcnow() → datetime.now(UTC) (deprecated 3.12)
• datetime.utcfromtimestamp() → datetime.fromtimestamp(ts, UTC) (deprecated 3.12)
• imp module → importlib (removed 3.12)
• typing.List, typing.Dict → list, dict (3.9+)
• typing.Optional[X] → X | None (3.10+)
• typing.Union[X, Y] → X | Y (3.10+)

Search for deprecated patterns:

# Find deprecated datetime usage
grep -rn "datetime.utcnow\|datetime.utcfromtimestamp" --include="*.py" .

# Find old typing imports
grep -rn "from typing import.*List\|from typing import.*Dict\|from typing import.*Optional" --include="*.py" .

# Find old collections imports
grep -rn "from collections import.*Callable\|from collections import.*Iterable" --include="*.py" .

Verification Checklist

• [ ] uv is used for venv creation and package installation
• [ ] pyproject.toml is the single configuration source (no setup.py/setup.cfg)
• [ ] requires-python = ">=3.13" is set in pyproject.toml
• [ ] ruff check . --select UP reports no issues (or only accepted exceptions)
• [ ] No deprecated datetime.utcnow() or datetime.utcfromtimestamp() usage
• [ ] No old-style typing imports (List, Dict, Optional, Union)
• [ ] CI/CD updated to use uv
• [ ] README.md reflects uv-based setup instructions
• [ ] All tests pass after modernization

Examples

Example: Migrate pip to uv

1. Check current setup:
   - ls -la | grep -E "setup.py|requirements.txt|pyproject.toml"
   - cat pyproject.toml

2. Install uv (if not already installed):
   - Via package manager: sudo zypper install uv  # openSUSE
   - Or as user package: pip install --user uv

3. Test uv with current project:
   - uv venv
   - source .venv/bin/activate
   - uv pip install -e ".[dev]"
   - pytest (verify all tests pass)

4. Update CI/CD:
   - Edit .github/workflows/test.yml
   - Replace pip commands with uv

5. Update README:
   - Replace pip instructions with uv

6. Commit: "Migrate from pip to uv for dependency management"

Example: Modernize syntax to Python 3.13

1. Update pyproject.toml:
   [project]
   requires-python = ">=3.13"

2. Run pyupgrade:
   pyupgrade --py313-plus **/*.py

3. Review changes:
   git diff
   # Check: List[X] → list[X], Union[X, Y] → X | Y, etc.

4. Run ruff for additional upgrades:
   ruff check . --select UP --fix

5. Verify type checking still works:
   mypy .
   basedpyright .

6. Run tests:
   pytest

7. Commit: "Modernize syntax to Python 3.13+"

Example: Complete modernization

1. Migrate to uv (see Example 1)

2. Consolidate configuration:
   - Read setup.py and setup.cfg
   - Migrate all config to pyproject.toml
   - Remove setup.py and setup.cfg
   - Verify: uv pip install -e ".[dev]"

3. Modernize syntax (see Example 2)

4. Update deprecated APIs:
   - grep -r "from collections import.*Iterable" .
   - Replace with collections.abc
   - grep -r "datetime.utcnow" .
   - Replace with datetime.now(UTC)

5. Final validation:
   - ruff check . --select UP (clean)
   - pytest (all pass)
   - mypy . && basedpyright . (no errors)

6. Update documentation:
   - README reflects uv usage
   - CONTRIBUTING.md updated

7. Commit: "Modernize codebase: uv, Python 3.13 syntax, pyproject.toml"

Related Skills

• Prerequisites: py-quality-setup (tool configuration), py-test-quality (safety net before syntax changes)
• Enforcement: py-git-hooks (enforce modern syntax via ruff UP rules)
• See also: py-complexity (modernization often enables simplification)

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: l-mb
• Source: l-mb/python-refactoring-skills
• License: MIT

Install and usage instructions live in the source repository linked above.