Python3.5:使用inheritan初始化类

Question

我最近偶然发现了Python中的元类，并决定使用它们来简化一些特性。（使用Python3.5）

简而言之，我正在编写一个模块，定义必须注册和初始化的类，例如“组件”（components）（我的意思是我需要初始化实际的类，而不是实例）。在

我可以轻松注册课程：

class MetaComponent(type):
    def __init__(cls, *args, **kargs):
        super().__init__(*args, **kargs)
        RegisterComponent(cls)

class BaseComponent(metaclass=MetaComponent):
    pass

class Component(BaseComponent):
    """This is the actual class to use when writing components"""

在本例中，我注册了组件的类，因为它允许我以后引用它们，而不需要实际引用它们。在

但是类缺乏初始化自身的能力（至少在Python3.5中是这样），并且会导致一些问题，例如：

^{pr2}$

现在，这是一个问题，因为我们的想法是每个经理有一个唯一的子经理列表。但是SubManager字段在每个子类中共享。。。所以把自己的名单加在每个人的名单上都会增加。在

所以下一个想法是实现一种初始化器：

class BaseManager(Component):
    @classmethod
    def classinit(cls):
        cls.SubManagers = []

但是现在，我需要一种在类创建之后调用这个方法的方法。因此，让我们再次对元类执行此操作：

class MetaComponent(type):
    def __init__(cls, *args, **kargs):
        super().__init__(*args, **kargs):
        cls.classinit(**kargs)
        RegisterComponent(cls)

class BaseComponent(metaclass=MetaComponent):
    @classmethod
    def classinit(cls, **kargs):
        print('BASE', cls)

class Component(BaseComponent):
    @classmethod
    def classinit(cls, **kargs):
        super().classinit(**kargs) # Being able to use super() is the goal
        print('COMPONENT', cls)

我认为我已经结束了这件事。在我看来，这是一种优雅的方法。将从创建的每个类中调用classinit()（不同于在父类上调用的3.6__init_subclass__）。至少我喜欢它，直到Python3.5在RuntimeError: super(): empty __class__ cell中大受欢迎。。。在

我读到它是因为我从元类的__init__方法中调用了一个方法，并且尽管类是创建的（因此我希望将代码放入__init__，以初始化已经创建的内容），但它缺少这个__class__单元格，至少在那时是这样的。。。在

我试着在Python3.6中运行完全相同的代码，但它起作用了，所以我猜出了问题，但得到了修复。。。在

我真正的问题是：

• Can we truly initialize classes with metaclasses in Python 3.5 ?
• Is there a way to avoid the use-restriction of super() in the initialization procedure?
• Why is it working in 3.6?
• If everything should fail, what would be the best course of action to still provide the class initialization, and allowing for super(...) calls? (Like do I need to refer to the super class explicitly ?)

提前谢谢你的帮助。在

编辑：

每个类的目标都是“能够很容易地从一个类中派生出一个组件：

class Manager(Component):
    def classinit(cls, **kargs):
        cls.SubManagers = []

    @classmethod
    def RegisterSubManager(cls, manager):
        cls.SubManagers.append(manager)
        return manager

@Manager.RegisterSubManager
class EventManager(Manager):
    def classinit(cls, **kargs):
        super().classinit(**kargs) # keep the old behaviour
        cls.Events = []

    # ...

@EventManager.RegisterSubManager
class InputManager(EventManager):
    def classinit(cls, **kargs):
        super().classinit(**kargs) # again, keep old behaviour
        cls.Inputs = []

    # use parts of EventManager, but define specialized methods
    # for input management

管理者是一个问题，我有多个依赖于组件和初始化类的能力的概念。在

Answer 1

好的，经过一些实验后，我设法提供了一个“修复”来允许类初始化，允许使用super()。在

首先，模块要“修复”初始化方法：

# ./PythonFix.py
import inspect
import types

def IsCellEmpty(cell):
    """Lets keep going, deeper !"""
    try:
        cell.cell_contents
        return False
    except ValueError:
        return True

def ClosureFix(cls, functionContainer):
    """This is where madness happens.
    I didn't want to come here. But hey, lets get mad.
    Had to do this to correct a closure problem occuring in
     Python < 3.6, joy.
    Huge thanks: https://stackoverflow.com/a/4885951/7983255
    """

    # Is the class decorated with @classmethod somehow
    isclassmethod = inspect.ismethod(functionContainer) and functionContainer.__self__ is cls
    if isclassmethod:
        function = functionContainer.__func__
    else:
        function = functionContainer

    # Get cells and prepare a cell holding ref to __class__
    ClosureCells = function.__closure__ or ()
    ClassCell_Fix = (lambda: cls).__closure__[0]

    # Shortcut
    c = function.__code__
    HasClassFreevar = '__class__' in c.co_freevars
    HasEmptyCells = any(IsCellEmpty(cell) for cell in ClosureCells)
    if HasClassFreevar and not HasEmptyCells: # No fix required.
        return classmethod(function)

    Freevars_Fixed = c.co_freevars
    Closure_Fixed = ClosureCells

    if not HasClassFreevar:
        Freevars_Fixed += ('__class__',)
        Closure_Fixed += (ClassCell_Fix,)

    elif HasEmptyCells: # This is silly, but for what I'm doing its ok.
        Closure_Fixed = tuple(ClassCell_Fix if IsCellEmpty(cell) else cell for cell in ClosureCells)

    # Now the real fun begins
    PyCode_fixedFreevars = types.CodeType(
        c.co_argcount, c.co_kwonlyargcount, c.co_nlocals,
        c.co_stacksize, c.co_flags, c.co_code, c.co_consts, c.co_names,
        c.co_varnames, c.co_filename, c.co_name, c.co_firstlineno,
        c.co_lnotab, Freevars_Fixed, c.co_cellvars
    )

    # Lets fetch the last closure to add our __class__ fix
    FixedFunction = types.FunctionType(
        PyCode_fixedFreevars, function.__globals__, function.__name__,
        function.__defaults__, Closure_Fixed
    )

    # Lets rewrap it so it is an actual classmethod (which it should be):
    return classmethod(FixedFunction)

现在，组件代码：

^{pr2}$

说句公道话，我很高兴能完成。希望这能帮助那些想要初始化类的人（至少在Python3.6之前的环境中……）。在