TypeError:在列表中使用'sum()'时,'NoneType'对象不可迭代

Question

我正进入(状态

TypeError: 'NoneType' object is not iterable

当我试图找到一个列表的总和.

出现问题的地方:

if(sum(self._candidates) + self._allCandidates[self._depth]._weight > 20):
    self._left = Node(self._candidates, self._depth + 1, self._allCandidates)
else:
    self._left = Node(self._candidates.append(self._allCandidates[self._depth]), self._depth + 1, self._allCandidates)

节点定义:

def __init__(self, candidates = [], depth = -1, allCandidates = []):
        self._candidates = candidates
        self._depth = depth
        self._allCandidates = allCandidates

感谢您对此事的任何帮助.

Answer 1

这是错的:

Node(self._candidates.append(self._allCandidates[self._depth])

来自的返回值.append是None错误.