返回列表时出错

Question

这是一个用于求一个数的因数之和的代码。查找因子函数中返回的列表是我猜 sum 函数无法访问的，因为当我打印列表时，它给出了正确的列表。

我收到的错误是：TypeError: object of type 'NoneType' has no len()

def perfect_number(n):
    def sum(list,counter,value):
        if counter==len(list):
            print (value)
        else:
            sum(list,counter+1,value+list[counter])
    def find_factors(n,a,list):
        if (a==n):
                        print (list,len(list))
            return (list)
        elif (n%a )== 0:
            list.append(a)                      
            find_factors(n,a+1,list)
        elif (n%a) !=0:
            find_factors(n,a+1,list)
    xyz = find_factors(n,1,[])
    return sum(xyz,0,0)



perfect_number(6)

Answer 1

您缺少一些返回语句：

def is_perfect_number(n):
    def sum_recursive(factors,counter,value):
        if counter==len(factors):
            return value
        else:
            return sum_recursive(factors, counter+1, value+factors[counter])

    def find_factors(n,a,factors):
        if (a==n):
            return
        elif (n%a) == 0:
            factors.append(a)                      
            find_factors(n,a+1,factors)
        elif (n%a) !=0:
            find_factors(n,a+1,factors)

    xyz = []
    find_factors(n, 1, xyz)
    return sum_recursive(xyz,0,0)==n

print is_perfect_number(6)
print is_perfect_number(28)
print is_perfect_number(228)