improving-python-code-quality

# Python Code Quality

## Quick Reference

| Tool | Purpose | Command |
|------|---------|---------|
| ruff | Lint + format | `ruff check src && ruff format src` |
| mypy | Type check | `mypy src` |

## Ruff Configuration

Minimal config in pyproject.toml:

```toml
[tool.ruff]
line-length = 88
target-version = "py310"

[tool.ruff.lint]
select = ["E", "W", "F", "I", "B", "C4", "UP"]
```

For full configuration options, see **[RUFF_CONFIG.md](RUFF_CONFIG.md)**.

## MyPy Configuration

```toml
[tool.mypy]
python_version = "3.10"
disallow_untyped_defs = true
warn_return_any = true
```

For strict settings and overrides, see **[MYPY_CONFIG.md](MYPY_CONFIG.md)**.

## Type Hints Patterns

```python
# Basic
def process(items: list[str]) -> dict[str, int]: ...

# Optional
def fetch(url: str, timeout: int | None = None) -> bytes: ...

# Callable
def apply(func: Callable[[int], str], value: int) -> str: ...

# Generic
T = TypeVar("T")
def first(items: Sequence[T]) -> T | None: ...
```

For protocols and advanced patterns, see **[TYPE_PATTERNS.md](TYPE_PATTERNS.md)**.

## Common Anti-Patterns

```python
# Bad: Mutable default
def process(items: list = []):  # Bug!
    ...

# Good: None default
def process(items: list | None = None):
    items = items or []
    ...
```

```python
# Bad: Bare except
try:
    ...
except:
    pass

# Good: Specific exception
try:
    ...
except ValueError as e:
    logger.error(e)
```

## Pythonic Idioms

```python
# Iteration
for item in items:           # Not: for i in range(len(items))
for i, item in enumerate(items):  # When index needed

# Dictionary access
value = d.get(key, default)  # Not: if key in d: value = d[key]

# Context managers
with open(path) as f:        # Not: f = open(path); try: finally: f.close()

# Comprehensions (simple only)
squares = [x**2 for x in numbers]
```

## Module Organization

```
src/my_library/
├── __init__.py      # Public API exports
├── _internal.py     # Private (underscore prefix)
├── exceptions.py    # Cu