Hi David, You posted your questions 3 days ago, so maybe you found a solution by now... but this might still be useful to you. I just implemented a visitor similar to yours, with a few changes. It involves the following objects: Order and OrderLineItem. I created a Folder named 'displayItemVisitor' in Order containing: Order.displayItemsVisitor.displayItem (Python Script): <params>item</params> return item.accept(container, _) Order.displayItemsVisitor.visitLineItem (DTML Method): <td>&dtml-qty;</td> <td class="price"><dtml-var "getRetailAmount(qty, in_basket_date)" fmt=dollars-and-cents></td> The 'accept' method of OrderLineItem is: <params>visitor, _</params> return visitor.visitLineItem(container, _) And the whole thing gets used in the DTML method that displays an order, using: <dtml-in line_items> <dtml-var "displayItemsVisitor.displayItem(_['sequence-item'], _)"> </dtml-in> Interesting points: - I'm passing _ explicitly instead of relying on binding. I vaguely recall reading something about a problem binding the namespace. It might be fixed in the latest Python Scripts, I haven't tried the CVS version yet. - visitLineItem is called in the context of an OrderLineItem, so no <dtml-with item> is needed. - If you wanted the visitor to implement looping over the items (which is how the GoF do it) you could easily make something like: Order.displayItemsVisitor.displayItems (DTML Method): <dtml-in line_items> <tr> <dtml-var "_['sequence-item'].accept(container, _)"> </tr> </dtml-in> BTW, I never thought of using a visitor for this until you brought it up, so thanks! What I really like about it is that the same 'accept' method can be used by multiple visitors, each one implementing a different view of the object. So I can have displayItemsVisitor, displayItemsCompactVisitor, and displayItemsEditableVisitor, all calling item.accept(), and I avoid polluting my OrderLineItem class with multiple view methods. OTOH, it requires adding public access methods to OrderLineItem, because a view method in OrderLineItem can do <dtml-var price>, while the visitor must do <dtml-var "getPrice()">. Oh well, there's always a price to pay ;-) HTH, Itai R. David Murray wrote:

OK, having helped me figure out how to work around the bug in accessing ZPatterns objects from a catalog, I've got a new challenge for you all.

Now that I've got my list of objects, I want to generate a web page displaying them. The page has the structure of a series of table rows. Inside each row data about a single object is displayed, using a common format but with certain differences depending on the type of object. To implement this, I am trying to use the Visitor pattern from the Gang of Four book.

So, I have a Folder displayItemList. This folder contains (at the moment) three methods: displayTable, visitAuthor, and visitBook. displayTable generates the html for the outer table, down to the <tr></tr> tags. Between those tags, it calls <dtml-var "accept(me)">, where me is this() for the displayTable method, and accept is a pythonscript method defined on each of the object type's Specialist. Each accept method is of the form:

return visitor.visitBook(None,_,item=context)

with _ bound to namespace on the bindings tab and 'visitor' being listed in the arguments line.

visitBook begins with the line:

<dtml-with item>

Trying to display my list, I get an AttributeError on 'validate', and ZDebug flags the 'with' line as the error location. validate appears nowhere in my code, so from all I can figure from a certain amount of inspection of the source, Zope is looking for this method on the DTMLMethod and not finding it.

ZDebug says the namespace stack consists of a single entry, which looks like the DTMLMethod itself (visitBook, presumably). Seems to me the namespace stack should be deeper than that.

I've been poking at this for a couple hours now without making any more progress, so I'm going to quit for the day and come back to it tomorrow. If anybody has any bright ideas, or sees something obvious I'm doing wrong, please clue me in. Thanks!

By the way, I also tried making accept be visitor.visitBook(context,_), but that produced the same error and ZDebug could only point to the call to accept as the error location.

--RDM -- -- Itai Tavor -- "Je sautille, donc je suis." -- itai@optusnet.com.au -- - Kermit the Frog --

-- "If you haven't got your health, you haven't got anything" --