What are some examples of type checking in Python 3.10?

What are some examples of type checking in Python 3.10?

In Python 3.10, type checking can be done using the new syntax for type hints. For example, you can use the | operator for union types. Here's a simple example:

def greet(name: str | None) -> str:
    if name is None:
        return 'Hello, World!'
    return f'Hello, {name}!'

This function accepts either a string or None as an argument.

Can you explain the new features related to type hints?

Sure! Python 3.10 introduced several enhancements for type hints, including:

1. Parenthesized context managers for better readability.
2. The | operator for union types, allowing you to specify multiple types more succinctly.
3. TypeGuard for more precise type narrowing in functions.

What is TypeGuard and how do I use it?

TypeGuard is a special type hint that allows you to create functions that narrow down types. Here's an example:

from typing import TypeGuard

def is_str_list(val: list) -> TypeGuard[list[str]]:
    return all(isinstance(i, str) for i in val)

This function checks if all elements in a list are strings and narrows the type accordingly.

Are there any other type checking tools I should know about?

Yes! Besides built-in type hints, you can use tools like mypy for static type checking, and Pyright for fast type checking in your IDE. These tools help catch type errors before runtime.