Type Hints & Annotations

from typing import Optional, Union, Any, TypeVar, Generic
from typing import List, Dict, Tuple, Set  # or use built-in types (3.9+)
from collections.abc import Callable, Generator, Sequence

# Function annotations
def greet(name: str, times: int = 1) -> str:
    return (f"Hello, {name}! " * times).strip()

# Optional (value or None)
def find_user(id: int) -> Optional[dict]:
    return db.get(id)  # might return None

# Union (multiple types)
def process(value: str | int) -> str:  # Python 3.10+ syntax
    return str(value)

# Generic types
def first(items: list[int]) -> int | None:
    return items[0] if items else None

# TypedDict
from typing import TypedDict

class User(TypedDict):
    id: int
    name: str
    email: str
    is_active: bool

# Dataclass with types
from dataclasses import dataclass

@dataclass
class Product:
    id: str
    name: str
    price: float
    stock: int = 0

from typing import TypeVar, Generic, Callable
from dataclasses import dataclass, field
from datetime import datetime

T = TypeVar("T")

@dataclass
class ApiResponse(Generic[T]):
    data: T
    status: int
    message: str
    timestamp: datetime = field(default_factory=datetime.now)

@dataclass
class User:
    id: int
    name: str
    email: str
    role: str = "viewer"

async def fetch_user(user_id: int) -> ApiResponse[User]:
    response = await http_client.get(f"/users/{user_id}")
    user_data = response.json()
    user = User(**user_data)
    return ApiResponse(
        data=user,
        status=response.status_code,
        message="User fetched successfully"
    )

# Usage — IDE knows the type!
result = await fetch_user(42)
print(result.data.name)  # IDE autocompletes .name