def shili(a,b):answer=[]for x in a:if x<=b/2:y=b-xif y in a :answer.append((x,y))return answera=[1,2,3,4,5,6,7,8,9]b=9c=shili(a,b)print(c)#输出结果：[(1, 8), (2, 7), (3, 6), (4, 5)]
