What are type hints and why use them?

Question

Accepted Answer

**Type hints** specify expected **types** for variables, arguments, and return values.

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

# Variables
age: int = 25
name: str = "Alice"
is_active: bool = True

# Collections
from typing import List, Dict, Optional, Union

def process(items: list[str]) -> dict[str, int]:
    return {item: len(item) for item in items}

def find_user(user_id: int) -> dict | None:
    if user_id in users:
        return users[user_id]
    return None

# Complex types
from typing import Callable, TypeAlias

Handler: TypeAlias = Callable[[str, int], bool]

def register_handler(handler: Handler) -> None:
    handlers.append(handler)

# TypedDict
from typing import TypedDict

class UserDict(TypedDict):
    name: str
    age: int
    email: str
```

**Benefits:**
- Better IDE support (autocompletion, error detection).
- Static analysis with mypy.
- Self-documenting code.
- Runtime: ignored by Python.

Python: What are type hints and why use them?