Add Python type annotations and type checking to template

[ktaletsk]

Description

Currently, the extension template includes comprehensive linting and type checking for JavaScript/TypeScript (ESLint, TypeScript compiler, Prettier, Stylelint), but the Python code lacks type annotations and type checking tooling.

Proposal

Phase 1: Add Type Annotations

Add type hints to all Python code in the template:

• Function parameters and return types
• Class attributes and methods
• Use modern Python typing features (typing module, Optional, Union, etc.)

Phase 2: Add Type Checker

Once type annotations are in place, add a type checker to verify them. Options:

Option 1: mypy (Community)

• Open-source type checker developed by the Python community
• De facto standard Python type checker
• Extensive configuration options
• Good for projects with gradual typing adoption
• Reference: https://github.com/python/mypy

Option 2: Ruff (Astral Software Inc.)

• Fast Python linter and formatter written in Rust
• Can replace multiple tools (flake8, black, isort, etc.)
• Growing type checking capabilities
• Single tool for multiple purposes
• Reference: https://github.com/astral-sh/ruff

Option 3: Pyright (Microsoft)

• Fast type checker from Microsoft
• Excellent IDE integration (native support in VS Code)
• Very fast and accurate
• Well-established in the ecosystem
• Reference: https://github.com/microsoft/pyright

Option 4: Pyrefly (Meta)

• Fast type checker and language server from Meta
• Ground-up rebuild (not based on Pyre)
• Combines type checking with language server features (code navigation, completion, semantic highlighting)
• Provides migration path from Pyright
• Reference: https://github.com/facebook/pyrefly

Benefits

• Type Safety: Catch type-related bugs before runtime
• Better IDE Support: Enhanced autocomplete, refactoring, and navigation
• Documentation: Types serve as inline documentation
• Consistency: Align Python code quality with existing JavaScript/TypeScript standards
• Modern Python: Follow current best practices (PEP 484+)

Implementation

1. Add type annotations to all Python files in template
2. Add tool dependencies to [project.optional-dependencies] in pyproject.toml.jinja
3. Add tool configuration sections to pyproject.toml.jinja
4. Update AGENTS.md with commands to run type checking
5. Consider adding pre-commit hooks or GitHub Actions for CI

[krassowski]

👍 to adding typing
👍 to mypy

Use modern Python typing features (typing module, Optional, Union, etc.)

Modern would be using | syntax not Union ;)

We currently have:

extension-template/template/pyproject.toml.jinja

Lines 8 to 10 in a55376f

	license = { file = "LICENSE" }
	requires-python = ">=3.9"
	classifiers = [

But Python 3.9 reaches EOL next week so it might make sense bump to 3.10 and make use of all typing features available.