Self, @override and Annotated
@override needs Python 3.12; Self needs 3.11. Annotated extras are visible only when asked for.
These tools describe specific shapes: TypedDict labels the keys of a dictionary, NamedTuple gives tuple fields names, Literal allows only listed values, Final marks a constant, and Self, Annotated and @override cover methods that return their own class, extra metadata and overriding.
Change the code and press Run (Ctrl+Enter). Predict what will happen first, then break it on purpose and read what changes. Your edits are saved and match the lesson page.
Ready for more? This phase has 5 hands-on exercises with automatic checks.
Practice questions
Write the code in the editor, run it, then open the model answer to compare.
Define a TypedDict named ToolCall with name: str and arguments: dict[str, str], create one, and print its __required_keys__ sorted.
Define a NamedTuple Rgb with r, g, b ints and print Rgb(255, 0, 0) and its g value.
Define a type Mode = Literal["fast", "slow"] and print its allowed values using get_args.
Explain it without notes
What is a TypedDict at run time, and what does it give you at all?
When would you use Literal instead of str?
Why is -> Self better than naming the class when a method returns self?
How does a NamedTuple differ from a plain tuple and from a dataclass?
Can you validate that a dictionary matches a TypedDict at run time with isinstance? What would you do instead?
Expected output
['a', '<b>', 'b']
Meow | __override__ = True
{'age': typing.Annotated[int, 'years', 0]}
metadata: ('years', 0)
plain: {'age': <class 'int'>}