pickle 加载错误“__init__() 恰好需要 2 个参数（给定 1 个）”

我的问题是自定义类已使用 pickle.dump 保存，因为这些文件已保存，自定义类已更改，现在当我使用 pickle.load 时出现此错误。是不是保存的文件有问题？

错误：

File "/cprprod/extern/lib/python2.7/pickle.py", line 1378, in load
return Unpickler(file).load()
File "/cprprod/extern/lib/python2.7/pickle.py", line 858, in load
dispatch[key](self)
file "/cprprod/extern/lib/python2.7/pickle.py", line 1070, in load_inst
self._instantiate(klass, self.marker())
File "/cprprod/extern/lib/python2.7/pickle.py", line 1060, in _instantiate
value = klass(*args)

我可以做些什么来加载文件吗？

代码

file = open(filename,'rb')
obj = pickle.load(file)

会给我错误。

这是一些可以重现错误的最小代码：

import pickle

class foo:
    def __init__(self,a):
        self.a = a

    def __str__(self):
        return str(self.a)

obj = foo(1)

with open('junk','wb') as f:
    pickle.dump(obj,f)

class foo:
    def __init__(self,a,b):
        self.a = a
        self.b = b
    def __str__(self):
        return '%s %s'%(self.a,self.b)

    def __getinitargs__(self):
        return (self.a,self.b)

with open('junk','rb') as f:
    obj = pickle.load(f)
    print str(obj)

鉴于我在问题中代表您发布的人为代码，我们可以“修复”此错误：

with open('junk','rb') as f:
    try:
        obj = pickle.load(f)
    except Exception as e:
        print e
        position = f.tell()
        a = foo.__getinitargs__
        del foo.__getinitargs__
        f.seek(position)
        obj = pickle.load(f)
        foo.__getinitargs__ = a

    print str(obj)

现在我们看到该实例已被 unpickled 并且不再具有属性b.