python - pickle 过程是确定性的吗？

Question

对于某个输入值，Pickle 是否总是产生相同的输出？我想在对内容相同但插入/删除历史记录不同的字典进行 pickle 时可能会出现问题。我的目标是使用 Pickle 和 SHA1 创建函数参数的“签名”，以实现记忆化。

Answer 1

I suppose there could be a gotcha when pickling dictionaries that have the same contents but different insert/delete histories.

右:

>>> pickle.dumps({1: 0, 9: 0}) == pickle.dumps({9: 0, 1: 0})
False

另请参阅:pickle.dumps not suitable for hashing

My goal is to create a "signature" of function arguments, using Pickle and SHA1, for a memoize implementation.

这有很多基本问题。想出一个正确映射相等性的对象到字符串的转换是不可能的——想想对象标识的问题:

>>> a = object()
>>> b = object()
>>> a == b
False
>>> pickle.dumps(b) == pickle.dumps(a)
True

根据您的具体要求，您可以将对象层次结构转换为可以散列的对象层次结构:

def hashablize(obj):
    """Convert a container hierarchy into one that can be hashed.
    
    Don't use this with recursive structures!
    Also, this won't be useful if you pass dictionaries with
    keys that don't have a total order.
    Actually, maybe you're best off not using this function at all."""
    try:
        hash(obj)
    except TypeError:
        if isinstance(obj, dict):
            return tuple((k, hashablize(v)) for (k, v) in sorted(obj.iteritems()))
        elif hasattr(obj, '__iter__'):
            return tuple(hashablize(o) for o in obj)
        else:
            raise TypeError("Can't hashablize object of type %r" % type(obj))
    else:
        return obj