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我正在尝试在 IronPython 中创建一个代理对象,它应该动态呈现底层结构。代理本身不应该有任何功能和属性,我试图在运行时捕获所有调用。捕获函数调用很容易,我只需要为我的对象定义getattr () 函数,并检查底层是否存在适当的函数,并返回一些类似函数的对象。

我的属性有问题 - 我不知道如何区分调用上下文,我的属性是被称为左值还是右值:

o = myproxy.myproperty #我需要调用underlying.myproperty_get()

或者

myproxy.myproperty = o #我需要调用underlying.myproperty_set(o)

我查看了 Python 中的特殊函数列表,但没有找到合适的。

我还尝试通过 exec() 和内置 property() 函数的组合在对象中动态创建属性,但我发现 IronPython 1.1.2 缺少整个“新”模块(在 IronPython 2.x 中存在) beta,但我宁愿使用 IP 1.x,因为 .NET 2.0 框架)。

有任何想法吗?

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2 回答 2

2

在 python 中你想要的通常实现是这样的:

class CallProxy(object):
    'this class wraps a callable in an object'
    def __init__(self, fun):
        self.fun = fun

    def __call__(self, *args, **kwargs):
        return self.fun(*args, **kwargs)

class ObjProxy(object):
    ''' a proxy object intercepting attribute access
    '''
    def __init__(self, obj):
        self.__dict__['_ObjProxy__obj'] = obj

    def __getattr__(self, name):
        attr = getattr(self.__obj, name)
        if callable(attr):
            return CallProxy(attr)
        else:
            return attr

    def __setattr__(self, name, value):
        setattr(self.__obj, name, value)

我写了一个测试来证明这符合预期:

#keep a list of calls to the TestObj for verification
call_log = list()
class TestObj(object):
    ''' test object on which to prove
        that the proxy implementation is correct
    '''
    def __init__(self):
        #example attribute
        self.a = 1
        self._c = 3

    def b(self):
        'example method'
        call_log.append('b')
        return 2

    def get_c(self):
        call_log.append('get_c')
        return self._c
    def set_c(self, value):
        call_log.append('set_c')
        self._c = value
    c = property(get_c, set_c, 'example property')

def verify(obj, a_val, b_val, c_val):
    'testing of the usual object semantics'
    assert obj.a == a_val
    obj.a = a_val + 1
    assert obj.a == a_val + 1
    assert obj.b() == b_val
    assert call_log[-1] == 'b'
    assert obj.c == c_val
    assert call_log[-1] == 'get_c'
    obj.c = c_val + 1
    assert call_log[-1] == 'set_c'
    assert obj.c == c_val + 1

def test():
    test = TestObj()
    proxy = ObjProxy(test)
    #check validity of the test
    verify(test, 1, 2, 3)
    #check proxy equivalent behavior
    verify(proxy, 2, 2, 4)
    #check that change is in the original object
    verify(test, 3, 2, 5)

if __name__ == '__main__':
    test()

这在 CPython 上执行,没有任何断言抛出异常。IronPython 应该是等价的,否则它会被破坏并且这个测试应该被添加到它的单元测试套件中。

于 2008-12-04T11:03:33.207 回答
2

尝试这个:

class Test(object):
    _test = 0

    def test():
        def fget(self):
            return self._test
        def fset(self, value):
            self._test = value
        return locals()
    test = property(**test())

    def greet(self, name):
        print "hello", name


class Proxy(object):
    def __init__(self, obj):
        self._obj = obj

    def __getattribute__(self, key):
        obj = object.__getattribute__(self, "_obj")
        return getattr(obj, key)

    def __setattr__(self, name, value):
        if name == "_obj":
            object.__setattr__(self, name, value)
        else:
            obj = object.__getattribute__(self, "_obj")
            setattr(obj, name, value)


t = Test()
p = Proxy(t)
p.test = 1
assert t.test == p.test
p.greet("world")
于 2008-12-04T12:07:00.520 回答