Function example of pair/legs of iterable. The type variable, T_, created with the TypeVar function, is used to clarify precisely how the legs() function restructures the data. The hint says that the input type is preserved on output. The input type is an Iterator of some arbitrary type, T_; the output will include tuples of the same type, T_. N…

legs.py

from typing import Iterator, Any, Iterable, TypeVar, Tuple

T_ = TypeVar('T_')
Pairs_Iter = Iterator[Tuple[T_, T_]]

def legs(iterable: Iterator[T_]) -> Pairs_Iter:
    begin = next(iterable)
    for end in iterable:
        yield begin, end
        begin = end

Usage:

list(legs(x for x in range(3)))
# [(0, 1), (1, 2)]

list(legs(iter([0, 1, 2])))
# [(0, 1), (1, 2)]