这里使用永久ID解决的酸洗问题是什么？

Pickle Stream具有内部引用的概念-如果同一对象在流中多次出现，则它只存储一次，然后仅被引用。但是，这仅指已存储在流中的内容--引用不能指向流外的对象，如原始对象。Pickle数据流的内容在概念上是其原始数据的副本。

import pickle

bar = (1, 2)
foo = {1: 1, 2: (1, 1), 'bar': bar}

with open('foo.pkl', 'wb') as out_stream:  # open a data stream...
     pickle.dump((bar, foo), out_stream)   # ...for pickle data

with open('foo.pkl', 'rb') as in_stream:
     bar2, foo2 = pickle.load(in_stream)

assert bar2 is foo2['bar']  # internal identity is preserved
assert bar is not bar2      # external identity is broken

import pickle

# some object to persist
# usually, one would have some store or bookkeeping in place
bar = (1, 2)


# The create/load implementation of the persistent id
# extends pickling/unpickling
class PersistentPickler(pickle.Pickler):
    def persistent_id(self, obj):
        """Return a persistent id for the `bar` object only"""
        return "it's a bar" if obj is bar else None


class PersistentUnpickler(pickle.Unpickler):
    def persistent_load(self, pers_id):
        """Return the object identified by the persistent id"""
        if pers_id == "it's a bar":
           return bar
        raise pickle.UnpicklingError("This is just an example for one persistent object!")


# we can now dump and load the persistent object
foo = {'bar': bar}
with open("foo.pkl", "wb") as out_stream:
    PersistentPickler(out_stream).dump(foo)

with open("foo.pkl", "rb") as in_stream:
    foo2 = PersistentUnpickler(in_stream).load()

assert foo2 is not foo     # regular objects are not persistent
assert foo2['bar'] is bar  # persistent object identity is preserved

作为一个真实的例子，我以前的cpy2py module使用PICLE在不同的解释器之间交换数据。对于常规的类似值的对象，这意味着在一个解释器中序列化，在另一个解释器中反序列化。对于某些特殊的有状态对象，这意味着仅交换在所有连接的解释器中唯一标识该对象的永久ID。

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