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skills/implementing-features/languages/PYTHON.md

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+# Python Quality Standards
+
+**Load this file when:** Implementing features in Python projects
+
+## Validation Commands
+
+```bash
+# Linting
+ruff check . --fix
+
+# Formatting
+ruff format .
+
+# Tests
+pytest -v
+
+# Type Checking
+mypy . --ignore-missing-imports
+
+# Coverage
+pytest --cov --cov-report=html
+
+# Full Validation Pipeline
+ruff check . && ruff format . && mypy . && pytest
+```
+
+## Required Standards
+
+```yaml
+Code Style:
+  - Line length: 120 characters (configurable)
+  - Imports: Sorted with isort style
+  - Docstrings: Google or NumPy style
+  - Type hints: Everywhere (functions, methods, variables)
+
+Testing:
+  - Framework: pytest
+  - Coverage: >= 80%
+  - Test files: test_*.py or *_test.py
+  - Fixtures: Prefer pytest fixtures over setup/teardown
+  - Assertions: Use pytest assertions, not unittest
+
+Documentation:
+  - All modules: Docstring with purpose
+  - All classes: Docstring with attributes
+  - All functions: Docstring with args, returns, raises
+  - Complex logic: Inline comments for clarity
+
+Error Handling:
+  - Use specific exceptions (not bare except)
+  - Custom exceptions for domain errors
+  - Proper exception chaining
+  - Clean resource management (context managers)
+```
+
+## Quality Checklist
+
+**Before Declaring Complete:**
+- [ ] All functions have type hints
+- [ ] All functions have docstrings (Google/NumPy style)
+- [ ] No linting errors (`ruff check .`)
+- [ ] Code formatted consistently (`ruff format .`)
+- [ ] Type checking passes (`mypy .`)
+- [ ] All tests pass (`pytest`)
+- [ ] Test coverage >= 80%
+- [ ] No bare except clauses
+- [ ] Proper exception handling
+- [ ] Resources properly managed
+
+## Example Quality Pattern
+
+```python
+from typing import Optional
+from pathlib import Path
+
+def load_config(config_path: Path) -> dict[str, any]:
+    """Load configuration from YAML file.
+
+    Args:
+        config_path: Path to configuration file
+
+    Returns:
+        Dictionary containing configuration values
+
+    Raises:
+        FileNotFoundError: If config file doesn't exist
+        ValueError: If config file is invalid YAML
+    """
+    if not config_path.exists():
+        raise FileNotFoundError(f"Config not found: {config_path}")
+
+    try:
+        with config_path.open() as f:
+            return yaml.safe_load(f)
+    except yaml.YAMLError as e:
+        raise ValueError(f"Invalid YAML in {config_path}") from e
+```
+
+---
+
+*Python-specific quality standards for production-ready code*