Python：帮助提高递归函数

Question

我有以下函数，并且它不时地返回错误“全局名称x未定义”，它在跳转到return语句时发生。我希望帮助改进此代码而不会丢失功能。任何有识之士将不胜感激。

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

这可以帮助...

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