Thanks, this works. An additional question puzzles me, if default_code is part of product_product, why when using debug mode in the GUI you see "default_code" for object "product.template" instead of "product.product"?

Its a nice question E.M, this is happening because of a concept called "Delegation Inheritance/instance inheritance" in odoo, where the derived class inherits all the fields of super class but in its "table"(derived class) only new fields added will be stored, however, other inherited fields also can be accessed from the code for the derived object normally. Since, it is inheriting those fields so it can also be used in your views easily. But as its not being stored in corresponding derived table/object at database, you have to go to super class if you want to manually manipulate its value. You can find further details here: Delegation Inheritance