python - 是否可以修饰一个实例将被 pickle 的 Python 类？

Question

以下代码运行正确:

import pickle

class MyClass():   
    def __init__(self, arg):
        self.arg = arg

a = MyClass('my arg')
with open('/home/mahikeulbody/mypickle', 'wb') as file:
    pickle.dump(a, file)

但是添加一个装饰器来获得一个多实例类:

import pickle

def multiton(cls):
    instances = {}
    def getinstance(arg):
        if arg not in instances:
            instances[arg] = cls(arg)
        return instances[arg]
    return getinstance

@multiton
class MyClass():   
    def __init__(self, arg):
        self.arg = arg

a = MyClass('my arg')
with open('/home/michel/mypickle', 'wb') as file:
    pickle.dump(a, file)

产生以下错误:

pickle.dump(a, file)
_pickle.PicklingError: Can't pickle <class '__main__.MyClass'>: it's not the same object as __main__.MyClass

出了什么问题？

Answer 1

Pickle 必须能够直接加载该类。您的装饰器用工厂函数替换了该类，从而使 pickle 无法导入该类本身。

使用单独的工厂函数，而不是装饰器，返回“私有(private)”类(但仍然可以直接导入):

class _MyClass():   
    def __init__(self, arg):
        self.arg = arg

def MyClass(arg, instances={}):
    if arg not in instances:
        instances[arg] = _MyClass(arg)
    return instances[arg]