A generic typesafe in-place implementation of a sort3 algorithm in Python

sort3.py

from typing import Annotated, Callable, NamedTuple, Protocol, TypeVar


class MaxLength(NamedTuple):
    """
    Summary
    -------
    a data structure for annotating the maximum length of a list

    Attributes
    ----------
    value (int) : the maximum length of a list
    """
    value: int


class Comparable(Protocol):
    """
    Summary
    -------
    a protocol for comparable types
    """
    __lt__: Callable[..., bool]
    __gt__: Callable[..., bool]
    __le__: Callable[..., bool]
    __ge__: Callable[..., bool]
    __eq__: Callable[..., bool]
    __ne__: Callable[..., bool]


T = TypeVar('T', bound=Comparable)


def sort3(array: Annotated[list[T], MaxLength(3)]) -> list[T]:
    """
    Summary
    -------
    sorts an array of length 3 in-place

    Parameters
    ----------
    array (list[T]) : the array to be sorted

    Returns
    -------
    array (list[T]) : the sorted array
    """
    if array[1] < array[0]:
        array[0], array[1] =\
        array[1], array[0]

    if array[2] < array[1]:
        array[1], array[2] =\
        array[2], array[1]

        if array[1] < array[0]:
            array[0], array[1] =\
            array[1], array[0]

    return array