proxy object

[Mike Warren]

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Greetings,

I have a simplified example of what I want to do (which isn't
working), which basically boils down to this: I want to return a
``proxy'' object which delays the instantiation of
expensive-to-instantiated objects, but I want the object to -- after
the instantiation -- behave just like it would without the proxy.

This mostly works, but isinstance() fails, kind of: if the ``hack''
code below is enabled, then isinstance works but other things fail.
So:

1. is there some way to override isinstance behaviour? or:

2. is there some way to ``replace'' the proxy instance with the
``other'' instance?

3. what exactly is going on below? Why is there an AttributeError
about ``_something''?

Okay, here's the example (I'm obviously not doing the
delayed-instantiation business). Any hints?

,----
| class Proxy:
|     def __init__(self,obj,hack=0):
|         self._obj = obj
|         if hack:
|             self.__class__ = self._obj.__class__
| 
|     def __getattr__(self,name):
|         return getattr(self._obj,name)
| 
| class Foo:
|     def __init__(self):
|         self._something = "something"
| 
|     def something(self):
|         return self._something
| 
| 
| a = Foo()
| b = Proxy(a)
| c = Proxy(a,hack=1)
| 
| print a,b,c
| 
| print "b is Foo?", isinstance(b,Foo)
| print "c is Foo?", isinstance(c,Foo)
| 
| print b.something()
| print c.something()
`----


- -- 
mike [at] mike [dash] warren.com
<URL:http://www.mike-warren.com>
GPG: 0x579911BD :: 87F2 4D98 BDB0 0E90 EE2A  0CF9 1087 0884 5799 11BD



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