python 循环内的上一个和下一个值

Posted 2021-05-09

from itertools import tee, islice as slice, chain, izip as zip

def previous_and_next(iterable, fill_value=None):
    prevs, items, nexts = tee(iterable, 3)
    prevs = chain([fill_value], prevs)
    nexts = chain(slice(nexts, 1, None), [fill_value])
    return zip(prevs, items, nexts)