[Zope] UNEXPECTED: Acquisition.Explicit may acquire implicitly

[Pierre-Julien Grizel]

Dieter Maurer wrote:
> 
> While trying to understand, what the "bself= self.aq_explicit"
> in "OFS.DTMLMethod.__call__" should do, I detected an unexpected
> behaviour:
> 
>     usually, this "bself" acquires implicitly from
>     its container (though not from its context)
> 
> More precisely:
> 
>     if "bself.aq_self" is itself an implicit acquisition
>     wrapper, the "bself.aq_explicit" acquires implicitly
>     from "bself.aq_self.aq_parent".
> 
> The following Python module demonstrates the behaviour:
> 
> -------------------------------------------------------
> from Acquisition import Implicit
> 
> class C(Implicit): pass
> 
> b= C()
> b.i= 0
> b.d= C()
> b.h= C()
> 
> e_bd= b.d.aq_explicit
> try:
>     e_bd.i
>     print 'e_bd implicitly acquired i'
> except AttributeError: pass
> 
> e_bhd= b.h.d.aq_explicit
> try:
>     e_bhd.i
>     print 'e_bhd implicitly acquired i'
> except AttributeError: pass
> -------------------------------------------------------
> 
> At first, I thought this were a bug.
> At second thought, however, it appears to be quite
> natural, though unexpected:
> 
>     if o is self.__of__(parent), then
>     getattr(o.aq_explicit,k) = getattr(self,k).__of__(o)
> 
>     If "self" is an implicit wrapper itself,
>     then acquisition may be used to look up "k".
> 
> This implies, that the idiom
> 
>         <dtml-if "_.hasattr(o.aq_explicit,XXXX)">
> 
> cannot be used safely to test, whether "o" has attribute
> XXXX itself (rather than acquired it).
> We probably should have a standard function for this kind
> of test.



Mhhh .... Something like "<dtml-if "_.hasattr(o.aq_base,XXXX)">" ?




P.-J.



> 
> Dieter
> 
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