允许在迭代期间删除的自定义字典

允许在迭代期间删除的自定义字典

如您所述，您可以将要删除的项目存储在某处，并将其删除推迟到以后。然后，问题就变成了 何时 清除它们以及 如何
确保最终调用清除方法。答案是上下文管理器，它也是的子类

dict

。

class dd_dict(dict):    # the dd is for "deferred delete"    _deletes = None    def __delitem__(self, key):        if key not in self: raise KeyError(str(key))        dict.__delitem__(self, key) if self._deletes is None else self._deletes.add(key)    def __enter__(self):        self._deletes = set()    def __exit__(self, type, value, tb):        for key in self._deletes: try:     dict.__delitem__(self, key) except KeyError:     pass        self._deletes = None

用法：

# make the dict and do whatever to itddd = dd_dict(a=1, b=2, c=3)# now iterate over it, deferring deleteswith ddd:    for k, v in ddd.iteritems():        if k is "a": del ddd[k] print ddd     # shows that "a" is still thereprint ddd      # shows that "a" has been deleted

with

当然，如果您不处于阻塞状态，则立即删除。因为这是一个

dict

子类，所以它就像

dict

上下文管理器外部的常规对象一样工作。

您还可以将其实现为字典的包装类：

class deferring_delete(object):    def __init__(self, d):        self._dict = d    def __enter__(self):        self._deletes = set()        return self    def __exit__(self, type, value, tb):        for key in self._deletes: try:     del self._dict[key] except KeyError:     pass        del self._deletes    def __delitem__(self, key):        if key not in self._dict: raise KeyError(str(key))        self._deletes.add(key)d = dict(a=1, b=2, c=3)with deferring_delete(d) as dd:    for k, v in d.iteritems():        if k is "a": del dd[k]    # delete through wrapperprint d

如果需要的话，甚至可以使包装器类作为字典完全发挥作用，尽管这是更多的代码。

从性能角度来看，这当然不是一个胜利，但是从程序员友好的角度来看，我喜欢它。第二种方法应该稍微快一点，因为它没有在每次删除时测试标志。