# Python Type Hinting

Type hinting is a formal solution to statically indicate the type of a value within your Python code. It was specified in PEP 484 and introduced in Python 3.5.

## Basics

Type hints are defined using a colon `:` after the variable name and an arrow `->` after the function parameters for the return type.

```python
def greeting(name: str) -> str:
    return 'Hello ' + name
```

## Variable Annotation

```python
age: int = 25
name: str = "Alice"
```

## The `typing` Module

For more complex types, the `typing` module provides support. Note that in Python 3.9+, you can often use built-in collection types (like `list` and `dict`) directly instead of importing `List` and `Dict`.

```python
from typing import List, Dict, Optional, Union

# List of integers
numbers: List[int] = [1, 2, 3]

# Dictionary with string keys and integer values
scores: Dict[str, int] = {"Alice": 10, "Bob": 20}

# Optional type (can be int or None)
user_id: Optional[int] = None

# Union type (can be int or float)
result: Union[int, float] = 10.5
```

## Static Type Checking

Python is dynamically typed, so type hints are ignored at runtime. However, they are invaluable for static type checkers like `mypy`, IDEs, and linters to catch errors before running the code.

[[programming/python/python]]