如何在 Python 中伪造/代理一个类

我编写了一些包装器，其中有另一个对象作为属性。该包装器代理（转发）所有属性请求__getattr__ and __setattr__到存储为属性的对象。我还需要为我的代理提供什么，以便包装器在通常情况下看起来像包装的类？

我想我可能需要修复诸如继承之类的问题__repr__, ... 我还需要注意什么以及如何修复继承以便instanceof() works?

编辑：我尝试制作函数代理，但是由于我不完全理解配方，它失败了:(

setattr_=object.__setattr__
getattr_=object.__getattribute__

class Proxy(object):
    __slots__=["_func", "_params", "_kwargs", "_obj", "_loaded", "__weakref__"]
    def __init__(self, func, *params, **kwargs):
        setattr_(self, "_func", func)
        setattr_(self, "_params", params)
        setattr_(self, "_kwargs", kwargs)

        setattr_(self, "_obj", None)
        setattr_(self, "_loaded", False)

    def _get_obj(self):
        if getattr_(self, "_loaded")==False:
            print("Loading")
            setattr_(self, "_obj", getattr_(self, "_func")(*getattr_(self, "_params"), **getattr_(self, "_kwargs")))
            setattr_(self, "_loaded", True)

        return getattr_(self, "_obj")
    #
    # proxying (special cases)
    #
    def __getattribute__(self, name):
        return getattr(getattr_(self, "_get_obj")(), name)
    def __delattr__(self, name):
        delattr(getattr_(self, "_get_obj")(), name)
    def __setattr__(self, name, value):
        setattr(getattr_(self, "_get_obj")(), name, value)

    def __nonzero__(self):
        return bool(getattr_(self, "_get_obj")())
    def __str__(self):
        return str(getattr_(self, "_get_obj")())
    def __repr__(self):
        return repr(getattr_(self, "_get_obj")())

    #
    # factories
    #
    _special_names=[
        '__abs__', '__add__', '__and__', '__call__', '__cmp__', '__coerce__',
        '__contains__', '__delitem__', '__delslice__', '__div__', '__divmod__',
        '__eq__', '__float__', '__floordiv__', '__ge__', '__getitem__',
        '__getslice__', '__gt__', '__hash__', '__hex__', '__iadd__', '__iand__',
        '__idiv__', '__idivmod__', '__ifloordiv__', '__ilshift__', '__imod__',
        '__imul__', '__int__', '__invert__', '__ior__', '__ipow__', '__irshift__',
        '__isub__', '__iter__', '__itruediv__', '__ixor__', '__le__', '__len__',
        '__long__', '__lshift__', '__lt__', '__mod__', '__mul__', '__ne__',
        '__neg__', '__oct__', '__or__', '__pos__', '__pow__', '__radd__',
        '__rand__', '__rdiv__', '__rdivmod__', '__reduce__', '__reduce_ex__',
        '__repr__', '__reversed__', '__rfloorfiv__', '__rlshift__', '__rmod__',
        '__rmul__', '__ror__', '__rpow__', '__rrshift__', '__rshift__', '__rsub__',
        '__rtruediv__', '__rxor__', '__setitem__', '__setslice__', '__sub__',
        '__truediv__', '__xor__', 'next',
    ]

    @classmethod
    def _create_class_proxy(cls, theclass):
        """creates a proxy for the given class"""

        def make_method(name):
            def method(self, *args, **kw):
                return getattr(getattr_(self, "_get_obj")(), name)(*args, **kw)
            return method

        namespace={}
        for name in cls._special_names:
            if hasattr(theclass, name):
                namespace[name]=make_method(name)
        return type("%s(%s)"%(cls.__name__, theclass.__name__), (cls,), namespace)

    def __new__(cls, obj, *args, **kwargs):
        """
        creates an proxy instance referencing `obj`. (obj, *args, **kwargs) are
        passed to this class' __init__, so deriving classes can define an 
        __init__ method of their own.
        note: _class_proxy_cache is unique per deriving class (each deriving
        class must hold its own cache)
        """
        try:
            cache=cls.__dict__["_class_proxy_cache"]
        except KeyError:
            cls._class_proxy_cache=cache={}
        try:
            theclass=cache[obj.__class__]
        except KeyError:
            cache[obj.__class__]=theclass=cls._create_class_proxy(obj.__class__)
        ins=object.__new__(theclass)
        theclass.__init__(ins, obj, *args, **kwargs)
        return ins

if __name__=='__main__':
    def t(x, y):
        print("Running t")
        return x+y

    a=Proxy(t, "a", "b")
    print("Go")
    print(a+"c")

此方法很好地解决了这个问题：

对象代理（Python 配方） https://web.archive.org/web/20220819152103/http://code.activestate.com/recipes/496741-object-proxying/

您必须遵循的总体思想是，类上的大多数方法都是通过某种组合来访问的__getattr__ and __getattribute__要么在类本身上，要么在它的元类上，但这不适用于Python特殊方法，即以双下划线开头和结尾的方法，为了找到这些方法，它们必须是实际类上的实际方法，没有属性代理是可能的。

您必须提供哪些方法显然取决于代理类本身提供的哪些方法。您需要提供的特殊方法isinstance()是__instancecheck__ and __subclasscheck__ http://docs.python.org/reference/datamodel.html#customizing-instance-and-subclass-checks方法。为了repr()为了工作，您还必须定义一个适当的__repr__()关于代理类本身。