Question

在Python 3.5中，我做了一个非常简单的dict子类，它使用同义键（存储为字典属性）：

class synonymDict(dict):

    def __init__(self, synonyms=None, *args, **kwargs):
        dict.__init__(self, *args, **kwargs)
        self.synonyms = {} if synonyms is None else synonyms

    def __getitem__(self, name):
        return dict.__getitem__(self, self.synonyms.get(name, name))

    def __setitem__(self, name, value):
        dict.__setitem__(self, self.synonyms.get(name, name), value)

    def __repr__(self):
        return 'synonymDict(%s)' % dict.__repr__(self)

现在，想象一下我在myPackage.myTools中定义了这个类；我尝试了酸洗和酸洗（用于多处理），但是出现以下属性错误：

>>> from myPackage import myTools
>>> synonyms = dict(A='a', B='b')
>>> mymapped = myTools.synonymDict(synonyms)
>>> mymapped['A'] = 36
>>> mymapped
synonymDict({'a': 36})
>>> mymapped.synonyms
{'A': 'a', 'B': 'b'}
>>> import pickle
>>> pickle.loads(pickle.dumps(mymapped))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/users/ldog/glouvel/install/python3/LibsDyogen/myPhylTree.py", line 35, in __setitem__
    dict.__setitem__(self, self.synonyms.get(name, name), value)
AttributeError: 'synonymDict' object has no attribute 'synonyms'

为什么在去渍过程中出现此错误？我应该复制synonyms的副本吗？是子类问题还是名称空间问题？

Answer 1

根据此答案https://stackoverflow.com/a/46560454/4614641，我可以用一行代码解决问题：定义默认的synonyms class 属性。

新代码：

class synonymDict(dict):
    synonyms = {}  # Needed for unpickling!

    def __init__(self, synonyms=None, *args, **kwargs):
        dict.__init__(self, *args, **kwargs)
        self.synonyms = {} if synonyms is None else synonyms

    def __getitem__(self, name):
        return dict.__getitem__(self, self.synonyms.get(name, name))

    def __setitem__(self, name, value):
        dict.__setitem__(self, self.synonyms.get(name, name), value)

    def __repr__(self):
        return 'synonymDict(%s)' % dict.__repr__(self)

这是因为解开（请参见https://docs.python.org/3.5/library/pickle.html#pickling-class-instances）不会调用该类的__init__方法，而是会尝试先调用__setitem__ ！我已经重写了该方法，以调用仅在__init__ ...

中定义的属性

解开字典的子类时发生AttributeError

1 个答案: