Python：帮助改进递归函数

Question

我有以下功能，并且不时返回错误“全局名称'x'未定义”，当它跳转到return语句时会发生。我希望在不失去功能的情况下帮助改进此代码。任何见解将不胜感激。

 def label(tree, instance, class_labels):
     '''Returns the label at the end of every "branch" in the tree'''
     global x
     for row in tree:
        if row[0] == instance[row[1]]:
            if row[2][0] in class_labels:
                x = row[2][0]
                 return x
            else:
                x = label(row[2], instance, class_labels)
    return x

Answer 1

这可能会有所帮助......

def label(tree, instance, class_labels):
    '''Returns the label at the end of every "branch" in the tree'''
    last = None
    for row in tree:
        if row[0] == instance[row[1]]:
            if row[2][0] in class_labels:
                return row[2][0]
            next = label(row[2], instance, class_labels)
            if next is not None:
                 last = next
    return last