[Zope-dev] zope.component: calling an Interface and calling queryAdapter give differing results

[Chris Withers]

Jim Fulton wrote:
>>> No, it's not a bug. This is in fact a feature (like it or not).
>> While I respect that this feature may have been chosen carefully, it
>> nevertheless seems more like a misfeature.  Chris' expectation was
>> reasonable and ought not to be violated without a good cause.
> 
> queryAdapter is used to look up named adapters. 

It sure would be nice if it had a docstring that at least indicated that 
was its only intended purpose.

However, how should I go about adapting an object to an interface where 
there may or may not be an adapter registered?

The natural way would seem to be:

obj = ISomething(otherobj,default=None)

...but I seem to remember people finding reasons why implementing that 
would never be possible.

> It is also a simpler  
> version of queryMultiAdapter, which looks up adapters for multiple  
> objects. In neither of these cases does it make sense to consider the  
> interfaces already provided by the object being adapted.  

Why not? What if the name provided is None?
(and why isn't the name provided None by default, rather thab being ''?)

> It makes no  
> sense to me for queryAdapter to have different semantics depending on  
> whether the name argument is provided (and is non-blank).

Why would the semantics be different?

 From a use point of view, I'd only expect queryAdapter to consider 
looking for a named adapter if I actually provide a name. If I provide 
no name, it would seem logical to look up a non-named adapter. If 
looking up a non-named adapter, it would make sense if the object 
already provides the desired interfaces to just return the object.

I'd love to see where this expectation is faulty...

Chris

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