Delegate attribute requests to object

Rami Chowdhury rami.chowdhury at gmail.com
Thu Aug 13 18:07:41 CEST 2009


Perhaps I'm misunderstanding something, but I don't think that's really  
typical decorator behavior? Typically decorators, as I understand them,  
take an instance argument -- so you wouldn't be saying

	def __init__(self):
		self.decorated = Decorated()

you'd be saying

	def __init__(self, decorated):
		self.decorated = decorated

As for the attribute access, I believe you can override __getattr__ to do  
what you want:

> class Decorator:
> [snip]
> def __getattr__(self, request):
> 	return self.decorated.__getattr__(request)

The same thing should work for methods, although you may want to pass  
arguments through as well.

Is there a reason why, for this use, just making Decorator a subclass of  
Decorated (and only overriding the methods you need to be different)  
wouldn't work?

On Thu, 13 Aug 2009 08:50:47 -0700, Evan Kroske <e.kroske at gmail.com> wrote:

> I'm trying to use the decorator pattern in a program I'm developing. I  
> want
> to create a decorator object that works like the object it's decorating
> except for a few functions. However, I'd rather not hard-code all the
> identical functionality from the decorated object into the decorator  
> object.
> Is there a way I can intercept all the attribute and function requests  
> for
> the decorator and delegate them to the decorated object? Here's some  
> example
> code:
>
> class Decorator:
>>   def __init__():
>>    self.decorated = Decorated()
>>
>>  def newFunction():
>>    # Do something
>>    pass
>>
>>  def interceptRequests(request):
>>    return self.decorated.request()
>>
>> class Decorated:
>>  def __init__():
>>    self.variable = 10
>>
>>  def oldFunction():
>>    # Do something
>>    pass
>
>
> I want to be able to do something like this:
>
> objectA = Decorator()
>> objectB = Decorated()
>> assert objectA.oldFunction() == objectB.oldFunction() # No error
>>
>
> Is it possible (without inheritance)?
>
> --
> Evan Kroske
> http://welcome2obscurity.blogspot.com/
> The code, comments, and challenges of a novice
> software developer desperate for attention.



-- 
Rami Chowdhury
"Never attribute to malice that which can be attributed to stupidity" --  
Hanlon's Razor
408-597-7068 (US) / 07875-841-046 (UK) / 0189-245544 (BD)



More information about the Python-list mailing list