For a standard python application, you probably will not need more than one EditingContext, containing all your objects. Typically, you will delegate the building and servicing for that application-wide EditingContext to some central manager all your objects/widgets/whatever we have access to.
Additionally, you'll maybe need from time to time to create a child EditingContext, for example if you need to make some changes and processing in a pop-up window and want to propose a 'Cancel' button at any point of the process. See chapter 5 for details.