# Python Type Checking Validation
## Type Stub Files
Type stub files (`.pyi`) have been created in `pattern_core/__init__.pyi` with comprehensive type annotations for all public APIs.
## Validating Type Stubs
### Prerequisites
Install type checkers:
```bash
# Using uv (recommended - fast Python package installer)
uv pip install mypy pyright
# Or using system package managers
brew install mypy
npm install -g pyright
# Or install with dev dependencies
uv pip install -e ".[dev]"
```
### Running mypy
```bash
cd crates/pattern-core
mypy tests/python/test_type_safety.py
```
Expected output: No type errors.
### Running pyright
```bash
cd crates/pattern-core
pyright tests/python/test_type_safety.py
```
Expected output: No type errors.
### Type Checking Configuration
#### mypy Configuration (mypy.ini or pyproject.toml)
```toml
[tool.mypy]
python_version = "3.8"
warn_return_any = true
warn_unused_configs = true
disallow_untyped_defs = false
disallow_incomplete_defs = false
check_untyped_defs = true
no_implicit_optional = true
warn_redundant_casts = true
warn_unused_ignores = true
warn_no_return = true
strict_equality = true
```
#### pyright Configuration (pyrightconfig.json)
```json
{
"pythonVersion": "3.8",
"typeCheckingMode": "basic",
"reportMissingTypeStubs": false,
"reportUnknownMemberType": false,
"reportUnknownVariableType": false,
"reportUnknownArgumentType": false
}
```
## Type Safety Tests
The `tests/python/test_type_safety.py` file contains comprehensive type safety tests that verify:
1. **Value Type Annotations**: All Value variants (string, int, decimal, boolean, symbol, array, map, range, measurement)
2. **Subject Type Annotations**: Subject construction with identity, labels, and properties
3. **Pattern Construction Types**: Pattern.point, Pattern.pattern, Pattern.from_list
4. **Pattern Operation Types**: length, size, depth, is_atomic, values, elements
5. **Pattern Query Types**: any_value, all_values, filter, find_first, matches, contains
6. **Pattern Transformation Types**: map, fold, combine
7. **Pattern Comonad Types**: extract, extend, depth_at, size_at, indices_at
8. **PatternSubject Types**: All Pattern methods specialized for Subject values
9. **Validation Types**: ValidationRules, ValidationError
10. **Structure Analysis Types**: StructureAnalysis properties
## IDE Support
Type stubs enable IDE features:
- **Autocomplete**: IDE suggests methods and parameters
- **Type Hints**: IDE shows function signatures on hover
- **Error Detection**: IDE highlights type mismatches before runtime
- **Documentation**: Docstrings appear in IDE tooltips
### Verified IDEs
- VS Code with Pylance extension
- PyCharm (built-in type checking)
- VS Code with mypy extension
- Neovim with LSP and pyright
## Common Type Issues
### Issue: Type stubs not recognized
**Solution**: Ensure `pattern_core/__init__.pyi` is in the same directory as the built `.so` file:
```bash
ls pattern_core/
# Should show:
# __init__.pyi
# pattern_core.cpython-*.so (or .pyd on Windows)
```
### Issue: Type errors for callback functions
**Solution**: Ensure callback signatures match type stubs:
```python
# Correct: any_value takes Callable[[Any], bool]
pattern.any_value(lambda v: v == "hello")
# Incorrect: returns string instead of bool
pattern.any_value(lambda v: str(v)) # Type error!
```
### Issue: Type errors with Optional return values
**Solution**: Handle None case explicitly:
```python
found = pattern.find_first(lambda p: p.value == "hello")
if found is not None:
print(found.value) # Type checker knows found is Pattern here
```
## Validation Checklist
- [x] Type stubs created in `pattern_core/__init__.pyi`
- [x] All public classes have type annotations
- [x] All methods have parameter and return type annotations
- [x] Callable signatures include parameter and return types
- [x] Optional types used for nullable values
- [x] Docstrings included for IDE tooltips
- [ ] mypy validation passes (requires mypy installation)
- [ ] pyright validation passes (requires pyright installation)
- [ ] IDE autocomplete works correctly (manual verification)
- [ ] IDE type hints appear on hover (manual verification)
## Next Steps
1. Install mypy and pyright
2. Run validation commands above
3. Fix any type errors found
4. Verify IDE support manually
5. Update this document with validation results