python中怎么表达等式

vc(t-1)和vc(t+1)表示时间(t-1）s和（t+1）对应的速度,vc是由多个数据组成

def fun(Vc, t):
    if 0<t<len(Vc)-1:
        if Vc[t-1]+Vc[t+1] == 0:
            return 0
    elif 1<t<len(Vc)-2:
        if Vc[t-2]+Vc[t+2] == 0:
            return 0
    else:
        return Vc[t]