Type Hints & Annotations

from typing import List, Dict, Optional, Union, Tuple, Callable

# Basic type hints
def greet(name: str) -> str:
    return f"Hello, {name}!"

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

# Collection types
def average(numbers: List[float]) -> float:
    return sum(numbers) / len(numbers)

# Optional (can be None)
def find_user(user_id: int) -> Optional[Dict[str, str]]:
    users = {1: {"name": "Alice"}, 2: {"name": "Bob"}}
    return users.get(user_id)

# Union types
def process(data: Union[str, int]) -> str:
    return str(data)

# Python 3.10+ syntax (cleaner!)
def process_new(data: str | int) -> str:
    return str(data)

# Callable type
def apply(func: Callable[[int, int], int], a: int, b: int) -> int:
    return func(a, b)

# Class with type hints
class User:
    def __init__(self, name: str, age: int, email: Optional[str] = None):
        self.name = name
        self.age = age
        self.email = email
    
    def to_dict(self) -> Dict[str, Union[str, int]]:
        return {"name": self.name, "age": self.age}

# Demo
print(greet("Alice"))
print(add(5, 3))
print(average([1.0, 2.0, 3.0]))
print(find_user(1))
print(apply(add, 5, 3))

user = User("Alice", 25, "alice@email.com")
print(user.to_dict())