[Zope] How can a method know if it was acquired?

[Dieter Maurer]

Itai Tavor wrote at 2003-7-7 20:00 +1000:
 > I got a folderish python product with the following method:
 > 
 >      def SKU(self):
 >          """ Return our SKU for the catalog """
 >          return self.sku
 > 
 > The problem is that when objects contained in instances of this product 
 > are cataloged, they acquire the SKU method, so they also get the sku 
 > property. That is bad. So what I need is something like this:
 > 
 >      def SKU(self):
 >          """ Return our SKU for the catalog """
 >          if (I was acquired):
 >              return None
 >          else:
 >              return self.sku
 > 
 > But I can't figure out how to do that. Help?

I fear this is impossible and would not be the right way either.

The right way (in my view) would be to make indexes manageable
and allow to set 3 boolean properties:

  ALLOW_ACQUISITION= 1 # to indicate that attributes may be acquired
  HIDE_EXCEPTIONS= 1   # silently ignore (most) exceptions during calls
  ALLOW_CALL= 1        # indicate that attributes are called when callable

I have implemented an "IndexBase" class that determines the value
of object "obj" for index "id" in the following way:

  def getValue(self,obj,default= None):
    '''the value of *obj* with respect to this index.'''
    marker= self

    # determine base value
    id= self.id
    if self.ALLOW_ACQUISITION:
      val= getattr(obj,id,default)
    elif hasattr(aq_base(obj), id): val= getattr(obj,id)
    else: val= default

    if safe_callable(val):
      if not self.ALLOW_CALL: return default
      try: val= val()
      except EXCEPTIONS_NOT_TO_BE_CAUGHT: raise
      except:
        if self.HIDE_EXCEPTIONS: return default
        raise
    return val


Dieter