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)