用于__getinitargs__的Python 3替代方案

Question

在Python 3的unpickling中，是否有足够短的方法来调用类的__init__构造函数？通常的方法是使用__getinitargs__，如此

from __future__ import print_function
import pickle

class Car:

    def __init__(self, model, number):
        self.model = model
        self.number = number
        print("constructed with", model, number)
        # many other things to do

    def __getstate__(self):
        # intentionally returns None
        pass

    def __setstate__(self, state):
        pass

    def __getinitargs__(self):
        # save some information when pickling
        # (will be passed to the constructor upon unpickling)
        return self.model, self.number

c = Car("toyota", 1234)
d = pickle.loads(pickle.dumps(c))
print("reconstructed with", d.model, d.number)

但是，新样式类和Python 3+中将忽略__getinitargs__，所有类只能是新样式类。有__getnewargs__但它只会将参数传递给不同的__new__类方法。上述说明性示例的python 2调用将导致

>> constructed with toyota 1234
>> constructed with toyota 1234
>> reconstructed with toyota 1234

虽然python 3调用会出错

>> constructed with toyota 1234
Traceback (most recent call last):
  File "test.py", line 26, in <module>
    print("reconstructed with", d.model, d.number)
AttributeError: 'Car' object has no attribute 'model'

并忽略__getinitargs__方法。

我认为Python 3在这方面不会轻易倒退，所以希望我错过了一些明显的东西。

编辑：用__getinitargs__替换__getnewargs__并不能解决问题。

Answer 1

如果您希望pickle通过调用Car(self.model, self.number)来取消对象的取消，通过__init__进行初始化，就像正常调用Car一样，然后告诉它在__reduce__ method中执行此操作：

def __reduce__(self):
    return (Car, (self.model, self.number))

Demo