如何挑選一個繼承自collections.deque的類？

Question

示例很清楚，我有一個繼承到deque的類和一個模塊'collections'的方法，有時我使用defaultdict，有些則不然。

>>> from collections import deque, defaultdict
>>> import pickle
>>> class lista(deque):
...         def __init__(self):
...             deque.__init__(self)
...             self.lib = defaultdict(dict)
... 
>>> p = lista()
>>> p.append("a")
>>> p.append("b")
>>> p.lib['t']=0
>>> p.__reduce__()
(<class '__main__.lista'>, (['a', 'b'], None), {'lib': defaultdict(<type 'dict'>, {'t': 0})})
>>> pik = pickle.dumps(p)
>>> unpik = pickle.loads(pik)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 1382, in loads
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 858, in load
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 1133, in load_reduce
TypeError: __init__() takes exactly 1 argument (3 given)
>>> 

最后一個問題，如何序列化這個對象？

Answer 1

Deque 初始化最多3個args ：

class collections.deque([iterable[, maxlen]])

在進行unpickling時，會提供所有三個（包括self），而__init__則不接受它們。 例如更改為

class lista(deque):
    def __init__(self, iterable=(), maxlen=None):
        deque.__init__(self, iterable, maxlen)
        self.lib = defaultdict(dict)