[web2py] Trouble with lazy virtual fields

[pbreit]

I am trying to use lazy virtual fields and cannot seem to get it to work. 
The non-lazy virtual fields work OK.

Also, can someone clear up the desirability of using lazy virtual fields. I 
saw a post where Massimo suggested there was no reason to make them lazy 
despite my understanding that laziness optimizes database access and/or 
performance.

This code:

class ItemVirtualFields(object):
    
    def currency_symbol(self):
        def lazy(currency=self.item.currency):
            if currency in ['USD', 'AUD', 'CAD']:
                return '$'
            elif currency=='GBP':
                return '£'
            elif currency=='EUR':
                return '€'
            else:
                return ''
        return lazy

db.item.virtualfields.append(ItemVirtualFields())


{{=item.currency_symbol}}

Produces this output:

     <function lazy at 0x17403ab0>0.02