Question

我改变了 getitem 特殊方法，用python字典实现了perl的自动修复功能，如下所示：

class AutoVivification(dict):
        """Implementation of perl's autovivification feature."""

        def __getitem__(self, item):

                try:
                        return dict.__getitem__(self, item)

                except KeyError:
                        value = self[item] = type(self)()
                        return value

这非常有用，但是现在我找不到返回创建对象的字典原始类的方法。首先，有可能吗？

Answer 1

这是一种可以关闭该功能的方法：

class AutoVivification(dict):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.vivify = True
        self.root = self

    def __getitem__(self, item):
        try:
            return dict.__getitem__(self, item)
        except KeyError:
            if not self.root.vivify:
                raise
            value = self[item] = type(self)()
            value.root = self.root
            return value

    def unvivify(self):
        self.vivify = False

用法：

a = AutoVivification()
a['b']['c'] = 3
print(a)
a.unvivify()
print(a['b']['d'])

输出：

{'b': {'c': 3}}
Traceback (most recent call last):
  File "/Users/alexhall/Dropbox/python/books/sandbox/sandbox.py", line 25, in <module>
    print(a['b']['d'])
  File "/Users/alexhall/Dropbox/python/books/sandbox/sandbox.py", line 9, in __getitem__
    return dict.__getitem__(self, item)
KeyError: 'd'

更改类后如何动态返回

1 个答案: