Catch type errors early.

Install MyPy

```bash pip install mypy ```

Basic Type Checking

```python # code.py def greet(name: str) -> str: return f"Hello {name}!"

def add(a: int, b: int) -> int: return a + b

This will fail type check result = add("5", "3")

Run: mypy code.py ```

Optional Types

```python from typing import Optional

def find_user(user_id: int) -> Optional[str]: if user_id == 1: return "Tom" return None

user = find_user(1) if user is not None: print(user.upper()) ```

Collection Types

```python from typing import List, Dict, Tuple, Set

def process_names(names: List[str]) -> Dict[str, int]: return {name: len(name) for name in names}

def get_coordinates() -> Tuple[float, float]: return (40.7128, -74.0060)

def unique_numbers(nums: List[int]) -> Set[int]: return set(nums) ```

Generics

```python from typing import TypeVar, Generic, List

T = TypeVar('T')

class Stack(Generic[T]): def __init__(self) -> None: self.items: List[T] = [] def push(self, item: T) -> None: self.items.append(item) def pop(self) -> T: return self.items.pop()

stack = Stack[int]() stack.push(1) stack.push(2) ```

Protocol

```python from typing import Protocol

class Drawable(Protocol): def draw(self) -> None: ...

class Circle: def draw(self) -> None: print("Drawing circle")

def render(obj: Drawable) -> None: obj.draw()

circle = Circle() render(circle) # OK ```

MyPy Configuration

```ini # mypy.ini [mypy] python_version = 3.11 warn_return_any = True warn_unused_configs = True disallow_untyped_defs = True ```

Remember

- Run mypy before committing - Type hints improve code clarity - Optional makes None explicit