TypedDict, Literal, NamedTuple and Final at run time
At run time a TypedDict is a dict, nothing is enforced, and the class remembers which keys are required.
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
{'role': 'user', 'content': 'Hello'} dict
is a plain dict: True
bad role is accepted at run time: {'role': 'robot', 'content': 'x'}
required: ['content', 'role']
optional: ['name']
Options required: ['model']
roles: ('user', 'assistant', 'system')
Point(x=3, y=0) 3 0 {'x': 3, 'y': 0}
unpacked: 3 0
MAX_TOKENS = 4096
MAX_TOKENS now 1