元组内具有元组的整数之和

Question

I'm trying to return the sum of all elements on a set of tuples inside tuples, but the last value is always None , so I get

TypeError: unsupported operand type(s) for +: 'int' and 'NoneType'

using the code below.

How do I skip this last value?

It has to be done with recursion.

L = (1, (2, (3, None)))

def sum(L):
    if not L:
        return None
    else:
        return L[0] + sum(L[1])

Answer 1

If that is really the structure of your tuple, just return zero when you reach the end:

def my_sum(L):
    if not L:
        return 0
    else:
        return L[0] + my_sum(L[1])

And don't shadow the name of a built-in. It's bad practice, even if it's technically legal.

Also, I don't think this is necessarily a good candidate for recursion. An iterative solution works the same, and without creating a new stack frame for every level:

s = 0
while L:
    s += L[0]
    L = L[1]

That's just a personal bonus for when you can make the design decision.

Answer 2

In [117]: L = (1, (2, (3, None)))
     ...:
     ...: def sum(L):
     ...:     if not L:
     ...:         return 0
     ...:     else:
     ...:         return L[0] + sum(L[1])
     ...:

In [118]: sum(L)
Out[118]: 6