code: def add_formatted_field(cls, field, format_string, title=''):
          
          global klass_count
          klass_count += 1
          fn_name = 'dyn_fn_%d' % klass_count
          cls.list_display.append(fn_name)
  
          if not title:
              title = field.capitalize()
  
          # python scoping is a bit weird with default values, if it isn't
          # referenced the inner function won't see it, so assign it for use
          _format_string = format_string
  
          def _ref(self, obj):
              return _format_string % getattr(obj, field)
          _ref.short_description = title
          _ref.allow_tags = True
          _ref.admin_order_field = field
  
          setattr(cls, fn_name, _ref)
docs: Adds a ``list_display`` attribute showing a field in the object
          using a python %formatted string.
  
          :param field:
              Name of the field in the object.
  
          :param format_string:
              A old-style (to remain python 2.x compatible) % string formatter
              with a single variable reference. The named ``field`` attribute
              will be passed to the formatter using the "%" operator. 
  
          :param title:
              Title for the column of the django admin table.  If not given it
              defaults to a capitalized version of ``field``