大数相乘

def fun(num1,num2):
    #num1 type str
    #num2 type str
    a = map(int,list(reversed(num1)))
    b = map(int,list(reversed(num2)))
    result = [0]*(len(a) + len(b))
    for ia,va in enumerate(a):
        c = 0
        for ib,vb in enumerate(b):
            tmp = va*vb + c + result[ia+ib] 
            result[ia+ib] = tmp % 10
            c = tmp / 10
        result[ia+ib+1] = c
    result = result[::-1]
    return result