How do I use the Proxy recipe ?

[English, Mark]

The proxy recipe
http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/252151 (*) by
Goncalo Rodrigues shows how to wrap an existing instance of a new or old
style class in a "Proxy" instance.
I'm just wondering what a programmer does once that's been achieved ? Is
he or she supposed to patch the generated proxy instance (or proxy
class) after it's been created ?

I may have missed the point, but I ended up allowing the caller to
"proxy()" to specify a base class. Code included below. Original code
from the recipe, all mistakes are mine. Proxy renamed to ProxyBase.

Thanks,
Mark

class ProxyBase(object):
    """base clas for all proxies"""
    def __init__(self, obj):
        super(ProxyBase, self).__init__(obj)
        self._obj = obj

    def __getattr__(self, attrib):
        return getattr(self._obj, attrib)

def make_binder(unbound_method):
    def f(self, *a, **k): return unbound_method(self._obj, *a, **k)

known_proxy_classes = {}

def proxy(obj, klassProxy=None, *specials):
    """factory-function for a proxy able to delegate special methods"""
    if klassProxy is None: #If no proxy class provided
        klassProxy = ProxyBase
    #do we already have a suitable customized class around ?
    obj_cls = obj.__class__
    key = obj_cls, klassProxy, specials
    cls = known_proxy_classes.get(key)
    if cls is None:
        #we don't have a suitable class around, so let's make it
        cls = type("%sProxy" % obj_cls.__name__, (klassProxy,), {})
        for name in specials:
            name = '__%s__' % name
            unbound_method = getattr(obj_cls, name)
            setattr(cls, name, make_binder(unbound_method))
        #also cache it for the future
        known_proxy_classes[key] = cls
    #instantiate and return the needed proxy
    return cls(obj)

class FooProxy(ProxyBase):
    def fn2(self):
        print 'Proxy foo2'
        print 'Proxy calling base...'
        self._obj.fn2()
        print 'Proxy called base...'

if __name__ == '__main__':
    #Quick example
    class Foo(object):
        def fn1(self): print 'Foo fn1'
        def fn2(self): print 'Foo fn2'
        def fn3(self): print 'Foo fn3'
    f = Foo()
    pf = proxy(f, FooProxy)
    pf.fn1()
    pf.fn2()

---Output---
Foo fn1
Proxy foo2
Proxy calling base...
Foo fn2
Proxy called base...

*I'm actually using the Python Cookbook, 2d ed., by Alex Martelli, Anna
Martelli Ravenscroft, and David Ascher (O'Reilly Media, 2005)
0-596-00797-3 recipe 6.6
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