如何在Python中伪造/代理一个类

Question

我写了一些包装器,它有另一个对象作为属性.此包装代理(向前)所有的属性与请求__getattr__和__setattr__存储作为属性的对象.我还需要为我的代理提供什么,以便在通常情况下包装器看起来像包装类？

我想我需要修复诸如继承之类的东西,也许__repr__,......我还需要处理什么,以及如何修复继承以便instanceof()有效？

编辑:我尝试制作一个功能代理,但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")

Answer 1

这个配方可以很好地解决这个问题:

对象代理(Python配方)

你必须遵循的总体思路是,在类的大多数方法是通过一些组合访问__getattr__和__getattribute__无论是在类本身,或在其元类,但这并不适用于蟒蛇的特殊方法,即开始进行一和双下划线结束,对于那些被发现的,它们必须是实际类的实际方法,不可能进行属性代理.

您必须提供哪些方法显然取决于代理类本身提供哪些方法.您需要提供的特殊方法isinstance()是__instancecheck__和__subclasscheck__方法.为了repr()工作,您还必须__repr__()在代理类本身上定义适当的.

Answer 2

通常,您可以使用wrapt库(pypi),它为您提供繁重的工作:

wrapt模块非常关注正确性.因此,它超越了现有机制,如functools.wraps(),以确保装饰器保持内省,签名,类型检查能力等[...]

为确保开销尽可能小,C扩展模块用于性能关键组件

它支持创建自定义包装类.为了添加自己的属性,您需要以wrapt不会尝试将它们传递给包装实例的方式声明它们.您可以:

• 使用前缀_self_添加属性并添加访问属性
• 除了in之外,在类级别声明属性 __init__

• 如果适合您的课程(在文档中未提及),请使用插槽,如下所示:

  class ExtendedMesh(ObjectProxy):
      __slots__ = ('foo')
  
      def __init__(self, subject):
          super().__init__(subject)
          self.foo = "bar"
  

它还支持函数包装器,它可能适合您的目的.