multimethods decorator

[Gerardo Herzig]

Bruno Desthuilliers wrote:

>gherzig at fmed.uba.ar a écrit :
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>
>>>Gerardo Herzig a écrit :
>>>      
>>>
>>>>Hi all. Im reading the Gido's aproach using decorators at
>>>>http://www.artima.com/weblogs/viewpost.jsp?thread=101605
>>>>
>>>>It looks good to me, but the examples shows the functionality using
>>>>functions.
>>>>Now, when i try to give this decorator into a method, if i try the
>>>>
>>>>class test(object):
>>>>   @multimethod(...)
>>>>   def met(self, ...):
>>>>
>>>>The multimethod decorator needs the types of the arguments, and, if the
>>>>met method requires self as the first argument, the multimethod should
>>>>look like
>>>>@multimethod(self.__class__, bla, ble) or some like that...
>>>>
>>>>Now i know that im wrong, because i have this error
>>>> >@multimethod(self.__class__)
>>>> >NameError: name 'self' is not defined
>>>>        
>>>>
>>>Indeed. Neither self (which will only be known at method call time) nor
>>>even the 'test' class (which is not yet defined when the decorator is
>>>executed) are availables.
>>>      
>>>
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>>Doh!
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>>
>
>If you're surprised, then you'd better learn way more about Python's 
>internal (execution model && object model mostly) before continuing with 
>multimethods.
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Is not that, is just...it allways make sense to me AFTER someone tells 
me!! :)

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>>>>So what would be the first argument to @multimethod??
>>>>        
>>>>
>>>A string ?-)
>>>      
>>>
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>>Ah? And what will that string contains?
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>
>What makes sens for you. Don't forget that Python has very strong 
>introspection features. Also note that it's not uncommon to use a 2-pass 
>approach : marking some methods with the decorator, then doing the real 
>processing in the metaclass (which of course implies a custom metaclass) 
>or in the __new__ method (in which case this processing will happen on 
>*each* instanciation).
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Oh well, now you kill me with that one.

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>>>FWIW, there's already an implementation of multiple dispacth by Mr. Eby...
>>>      
>>>
>>Oh yes, i found the dispatch version of multimethods, but i have not tried
>>it yet. Do you think is better this version than Guido's?
>>    
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>I think that dispatch is actually used in a few packages, frameworks or 
>applications. Is it the case of Guido's stuff ?
>
>Also, IIRC, Guido's snippet is quite less generic than dispatch (which 
>is based on expression rules, not only on types).
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Ok. So im giving dispatch version a chance. Its working nice so far. 
Thanks Man!
Gerardo