import itertools
from typing import TypeVar, Iterator, Tuple

T = TypeVar("T")


def pairwise(iterable: Iterator[T]) -> Iterator[Tuple[T, T]]:
    """s -> (s0,s1), (s1,s2), (s2, s3), ..."""
    a, b = itertools.tee(iterable)
    next(b, None)
    return zip(a, b)