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。
