deepcopy 不尊重元类

我有一堂课，根据设计，必须遵循单例图案。所以我继续使用元类。一切都运行良好，直到报告了一个错误，总而言之，deepcopy-ied 我的实例单例类不是相同的实例。

我可以通过从基础继承来解决这个错误单例-type 类，但我宁愿不这样做，原因在这个问题 https://stackoverflow.com/q/6760685/312650.

下面给出了该问题的一个工作示例：

class SingletonMeta(type):
    def __init__(cls, name, bases, dict):
        super(SingletonMeta, cls).__init__(name, bases, dict)
        cls.instance = None 
    def __call__(cls,*args,**kw):
        print "SingletonMeta __call__ was called"
        if cls.instance is None:
            cls.instance = super(SingletonMeta, cls).__call__(*args, **kw)
        return cls.instance

class MyClass1(object):
    __metaclass__ = SingletonMeta

class SingletonBase(object):
    _instance = None
    def __new__(class_, *args, **kwargs):
        print "SingletonBase __new__ was called"
        if not isinstance(class_._instance, class_):
            class_._instance = object.__new__(class_, *args, **kwargs)
        return class_._instance

class MyClass2(SingletonBase):
  pass

from copy import deepcopy as dcp

mm1 = MyClass1()
mm2 = dcp(mm1)
print "mm1 is mm2:", mm1 is mm2

mb1 = MyClass2()
mb2 = dcp(mb1)
print "mb1 is mb2:", mb1 is mb2

Output:

SingletonMeta __call__ was called
mm1 is mm2: False
SingletonBase __new__ was called
SingletonBase __new__ was called
mb1 is mb2: True

您能给我一些建议，告诉我应该如何解决这个问题吗？我正在运行 Python 2.7.X

上的文档copy模块这样说：

为了让类定义自己的复制实现，它可以定义特殊方法__copy__() and __deepcopy__()。 [...] 调用后者来实现深拷贝操作；它传递一个参数，即备忘录字典。 [...]

所以如果你声明这些返回self，这应该可以解决问题。