Python构造函数和默认值

Question

不知何故，在下面的 Node 类中，wordList 和 adjacencyList 变量在所有 Node 实例之间共享。

>>> class Node:
...     def __init__(self, wordList = [], adjacencyList = []):
...         self.wordList = wordList
...         self.adjacencyList = adjacencyList
... 
>>> a = Node()
>>> b = Node()
>>> a.wordList.append("hahaha")
>>> b.wordList
['hahaha']
>>> b.adjacencyList.append("hoho")
>>> a.adjacencyList
['hoho']

有什么办法可以让构造函数参数继续使用默认值(在这种情况下为空列表)，但让 a 和 b 都有自己的wordList 和 adjacencyList 变量？

我正在使用 python 3.1.2。

Answer 1

可变的默认参数通常不会做你想做的事。相反，试试这个:

class Node:
     def __init__(self, wordList=None, adjacencyList=None):
        if wordList is None:
            self.wordList = []
        else:
             self.wordList = wordList 
        if adjacencyList is None:
            self.adjacencyList = []
        else:
             self.adjacencyList = adjacencyList