Python练习题2：获得昨天和明天的日期

import sys from datetime import datetime,timedelta def next_1(date_str): start = datetime.strptime(date_str,'%Y-%m-%d') next_2 = timedelta(days = 1) return (start + next_2).strftime('%Y-%m-%d') def prev_1(date_str): start_2 = datetime.strptime(date_str,'%Y-%m-%d') next_2 = timedelta(days = -1) return (start_2 + next_2).strftime('%Y-%m-%d') while True: line = (sys.stdin.readline()).strip() if line == '': break print('前一天:', prev_1(line)) print('后一天:', next_1(line))