python 元类修改后的类无法进行持久化？

Z时代
2024-02-15
分类：IT

问题可能涉及的知识：

python 元类
python 数据持久化（pickle）
python 多线程（不一定）

我在进行python多进程操作时出现了问题
部分代码：

from multiprocessing import Process, Queue
from queue import Empty
def init(cls):
    def __init__(self, *args, **kwargs):
        queue = Queue()
        Process(target=process_main, args=(cls, queue, args, kwargs), daemon=True).start()
        map_fun_ = map_fun(queue)
        for i in dir(cls):
            if i not in not_transfer_fun and i[:2] == i[-2:] == '__' and callable(getattr(cls, i)):
                setattr(self, i, map_fun_(i))
    return __init__
class ProcessClassMeta(type):
    def __new__(cls, name, bases, attrs):
        self_cls = type(name, bases, attrs)
        cls = type(name, (object,), {'__init__': init(self_cls)})        return cls

测试部分代码：

from os import getpid
class B:
    def __init__(self):
        print(getpid())
        self.c = 'c'
    def a(self):
        print(getpid())
        self.c = 'a'
class A(B, metaclass=ProcessClassMeta):
    def b(self):
        print(getpid())
        self.c = 'b'
    def a(self):
        print(getpid())
        self.c = 'd'
print(getpid())
a = A()
print(a.c)
a.b()
print(a.c)
a.a()print(a.c)

输出：

5780
Traceback (most recent call last):
  File "D:/1/project/close2/ProcessClass.py", line 231, in <module>
    a = A()
  File "D:/1/project/close2/ProcessClass.py", line 190, in __init__
    Process(target=process_main, args=(cls, queue, args, kwargs), daemon=True).start()
  File "D:\1\python\WPy32-3770\python-3.7.7\lib\multiprocessing\process.py", line 112, in start
    self._popen = self._Popen(self)
  File "D:\1\python\WPy32-3770\python-3.7.7\lib\multiprocessing\context.py", line 223, in _Popen
    return _default_context.get_context().Process._Popen(process_obj)
  File "D:\1\python\WPy32-3770\python-3.7.7\lib\multiprocessing\context.py", line 322, in _Popen
    return Popen(process_obj)
  File "D:\1\python\WPy32-3770\python-3.7.7\lib\multiprocessing\popen_spawn_win32.py", line 89, in __init__
    reduction.dump(process_obj, to_child)
  File "D:\1\python\WPy32-3770\python-3.7.7\lib\multiprocessing\reduction.py", line 60, in dump
    ForkingPickler(file, protocol).dump(obj)_pickle.PicklingError: Can't pickle <class '__main__.A'>: it's not the same object as __main__.A

本代码是为了实现简化多进程操作，让多进程像单进程一样操作
我在元类中用type创建了一个类来替换原来的，于是就无法继续持久化用于传参了

回答：

from multiprocessing import Process, Manager
from os import getpid
def process_main(cls, dic, args, kwargs):
    instance = cls(*args, **kwargs)
    for attr in dir(cls):
        if attr[:2] == attr[-2:] == '__' and callable(getattr(cls, attr)):
            dic[attr] = getattr(instance, attr)
class B:
    def __init__(self):
        print(getpid())
        self.c = 'c'
    def a(self):
        print(getpid())
        self.c = 'a'
class A(B):
    def __init__(self, *args, **kwargs):
        self.manager = Manager()
        self.dic = self.manager.dict()
        Process(target=process_main, args=(A, self.dic, args, kwargs), daemon=True).start()
    def b(self):
        print(getpid())
        self.dic['c'] = 'b'
    def a(self):
        print(getpid())
        self.dic['c'] = 'd'
    @property
    def c(self):
        return self.dic.get('c')
print(getpid())
a = A()
print(a.c)
a.b()
print(a.c)
a.a()
print(a.c)