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 it
ddd = dd_dict(a=1, b=2, c=3)
# Now iterate over it, deferring deletes
with ddd:
for k, v in ddd.iteritems():
if k is "a":
del ddd[k]
print ddd # shows that "a" is still there
print 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 wrapper
print 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。
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