9

我想创建一个数据结构，其行为类似于字典，并具有一个附加功能，即跟踪哪些键已被“使用”。请注意，我不能在重复使用时弹出这些值。

该结构应支持这三种情况，即在访问时将密钥标记为已使用：

if key in d:
    ...
d[key]
d.get(key)

这是我写的：

class DictWithMemory(dict):

    def __init__(self, *args, **kwargs):
        self.memory = set()
        return super(DictWithMemory, self).__init__(*args, **kwargs)

    def __getitem__(self, key):
        self.memory.add(key)
        return super(DictWithMemory, self).__getitem__(key)

    def __contains__(self, key):
        self.memory.add(key)
        return super(DictWithMemory, self).__contains__(key)

    def get(self, key, d=None):
        self.memory.add(key)
        return super(DictWithMemory, self).get(key, d)

    def unused_keys(self):
        """
        Returns the list of unused keys.
        """
        return set(self.keys()).difference(self.memory)

由于我对dict的内部不是很熟悉，有没有更好的方法来实现这个结果？

4

1 回答 1

4

这是一个将元类中的所有内容抽象出来的解决方案。我不确定这是否真的更优雅，但如果您改变主意如何存储使用过的密钥，它确实提供了一些封装：

class KeyRememberer(type):

    def __new__(meta, classname, bases, classDict):
        cls = type.__new__(meta, classname, bases, classDict)

        # Define init that creates the set of remembered keys
        def __init__(self, *args, **kwargs):
            self.memory = set()
            return super(cls, self).__init__(*args, **kwargs)
        cls.__init__ = __init__

        # Decorator that stores a requested key in the cache
        def remember(f):
            def _(self, key, *args, **kwargs):
                self.memory.add(key)
                return f(self, key, *args, **kwargs)
            return _

        # Apply the decorator to each of the default implementations
        for method_name in [  '__getitem__', '__contains__', 'get' ]:
            m = getattr(cls, method_name)
            setattr(cls, method_name, remember(m))

        return cls


class DictWithMemory(dict):

    # A metaclass that ensures the object
    # has a set called 'memory' as an attribute,
    # which is updated on each call to __getitem__,
    # __contains__, or get.
    __metaclass__ = KeyRememberer

    def unused_keys(self):
        """
        Returns the list of unused keys.
        """
        print "Used", self.memory
        return list(set(super(DictWithMemory,
                              self).keys()).difference(self.memory))
于 2012-05-25T17:48:38.303 回答