How to type a Tuple with many elements in Python?

Question

I am experimenting with the typing module and I wanted to know how to properly type something like a Nonagon (a 9 point polygon), which should be a Tuple and not a List because it should be immutable.

In 2D space, it would be something like this:

Point2D = Tuple[float, float]
Nonagon = Tuple[Point2D, Point2D, Point2D, Point2D, Point2D, Point2D, Point2D, Point2D, Point2D]

nine_points: Nonagon = (
    (0.0, 0.0),
    (6.0, 0.0),
    (6.0, 2.0),
    (2.0, 2.0),
    (6.0, 5.0),
    (2.0, 8.0),
    (6.0, 8.0),
    (6.0, 10.0),
    (0.0, 10.0),
)

Is there any syntactic sugar available to make the Nonagon declaration shorter or easier to read?

This is not valid Python, but I am looking for something similar to this:

Nonagon = Tuple[*([Point2D] * 9)]  # Not valid Python

Or using NamedTuple

# Not properly detected by static type analysers
Nonagon = NamedTuple('Nonagon', [(f"point_{i}", Point2D) for i in range(9)])  

This is NOT what I want:

# Valid but allows for more and less than 9 points
Nonagon = Tuple[Point2D, ...]  

I think the most adequate way would be something like:

from typing import Annotated

# Valid but needs MinMaxLen and checking logic to be defined from scratch
Nonagon = Annotated[Point2D, MinMaxLen(9, 9)]  

Answer 1

You can use the types module. All type hints come from types.GenericAlias.

From the doc:

Represent a PEP 585 generic type
E.g. for t = list[int], t.__origin__ is list and t.__args__ is (int,).

This means that you can make your own type hinting by passing the type arguments to the class itself.

>>> Point2D = tuple[float, float]
>>> Nonagon = types.GenericAlias(tuple, (Point2D,)*9)
>>> Nonagon
tuple[tuple[float, float], tuple[float, float], tuple[float, float], tuple[float, float], tuple[float, float], tuple[float, float], tuple[float, float], tuple[float, float], tuple[float, float]]