[Zope3-dev] re: calling objects when evaluating path expressions

[Steve Alexander]

>> Conclusion 2: TALES should not try to call things at all. This should be 
>> left up to the Zope traversal components, so that the behaviour may be 
>> customised.
> 
> Now that we have properties, I see no reason to ever call things at
> all.  The call-if-callable behavior is a carryover from Zope2 and
> pre-new-style-classes Python, when it was really painful to provide a
> computed attribute.

I agree for TALES.


>>    3: Making the zope 3 default traversal machinery call an object on
>>       traversal if and only if the following conditions hold:
>> 
>>       a: the object provides no interfaces
>> 
>>       b: the object has a __call__ attribute
>> 
>>       c: on inspection, it appears that the __call__ attribute can be
>>          called with no arguments
>> 
>>    This will most usefully apply to instance methods, static methods,
>>    class methods and method-wrappers (which are how builtin methods
>>    appear to Python).
> 
> I'd propose to skip even this.  Or is that too radical?

I think that's too radical. Such a spartan (or is that explicit) 
approach would be fine if objects presented using page templates in Zope 
3 were always written afresh for Zope 3. However, one of the goals of 
Zope 3 is to allow pre-existing code, and code written for other 
purposes, to be presented from Zope 3.

So, I think Zope should provide facilities over and above TALES to call 
things that obviously should be called.

Users of page templates aren't necessarily python programmers. And, when 
we have a DTML that uses path expressions, users of DTML won't 
necessarily be python programmers. I think many of these users will 
appreciate a small amount of well-contained implicitness in exchange for 
making path expressions more concise.

--
Steve Alexander