MyProject/
   browser/
     templates/
       objectwidget.pt
     widgets.py
   shipping.py


MyProject/browser/widgets.py:

class ObjectWidget:
   template = "templates/objectwidget.pt"

MyProject/shipping.py

from browser.widgets import ObjectWidget

class SomeClass:
  def __init__(self):
    self.form_fields['address'].widget = ObjectWidget