pickle加载错误“__init__()取2个参数(给定1个)”

My issue is that a custom class has been saved with pickle.dump, since these files were saved the custom class has been changed and now when I use pickle.load I am getting this error. Is it a problem with the saved file?

我的问题是自定义类被保存为pickle。转储，因为这些文件被保存，所以自定义类已经被更改，现在当我使用pickle时。负载我得到这个错误。保存的文件有问题吗?

The error:

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)

Is there anything I can do to load the file?

我能做些什么来加载文件吗?

The code

的代码

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

will give me the error.

会给我错误。

Here is some minimal code which can reproduce the error:

下面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)

3 个解决方案

#1

Given the contrived code that I posted on your behalf in the question, we can "fix" this error as:

鉴于我在问题中以你的名义发布的设计代码，我们可以“修复”这个错误，如下所示:

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)

Now we see that the instance has been unpickled and no longer has attribute b.

现在我们看到实例已经被取消pickle，并且不再具有属性b。

#2

If you added __getinitargs__() then it is up to you to make sure your new class can handle the arguments passed to __init__(). Old data that doesn't have the __getinitargs__ data will still lead to __init__ to be called but with no arguments.

如果您添加了__getinitargs__()，那么您应该确保您的新类能够处理传递给__init__()的参数。没有__getinitargs__数据的旧数据仍然会导致__init__被调用，但没有参数。

Make the arguments to __init__ optional via keyword arguments:

通过关键字参数使__init__可选:

def __init__(self, otherarg=None):
    if otherarg is None:
        # created from an old-revision pickle. Handle separately.
        # The pickle will be loaded *normally* and data will still be set normally
        return
    self.otherarg = otherarg

When loading the old-style pickle, the data for these classes will still be restored. You can use __setstate__() to transform the internal state as needed.

当加载旧式pickle时，这些类的数据仍然会被恢复。您可以使用__setstate__()来转换需要的内部状态。

Alternatively, temporarily remove the __getinitargs__ method from the class:

或者，临时从类中删除__getinitargs__方法:

initargs = foo.__getinitargs__.__func__
del foo.__getinitargs__
obj = pickle.load(f)
foo.__getinitargs__ = initargs

and re-dump your pickles from the now-loaded objects with __getinitargs__ reinstated.

然后用恢复的__getinitargs__重新从当前加载的对象中转储泡菜。

I've tested both methods and in both cases the old data is loaded correctly and you can then dump your objects again to a new pickle file with __getinitargs__ just fine.

我已经测试了这两种方法，在这两种情况下，旧数据都被正确地加载了，然后您可以将对象再次转储到一个新的pickle文件中，并使用__getinitargs__。

#3

You might want to modify the custom class to optionally require a second parameter. This would keep back award compatibility with your pickled objects.

您可能希望修改自定义类，以便可以选择地需要第二个参数。这将保留与您的pickle对象的兼容性。

#1