When using the max(), min(), and sorted() functions, we have an optional key= parameter. The function provided as an argument value modifies the behavior of the higher-order function. In many cases, we used simple lambda forms to pick items from a tuple. Here are two examples we heavily relied on:
from typing import Callable, Sequence, TypeVar
T_ = TypeVar("T_")
fst: Callable[[Sequence[T_]], T_] = lambda x: x[0]
snd: Callable[[Sequence[T_]], T_] = lambda x: x[1]
These match built-in functions in some other functional programming languages that are used to pick the first or second item from a tuple. This includes type hints to assure that there's no other transformation going on—the type of items in the sequence is bound to the type variable, T_, which reflects the type of the result of the function.
We don't...
