Python 3 Object-Oriented Programming - Third Edition

An observer example

The observer pattern might be useful in a redundant backup system. We can write a core object that maintains certain values, and then have one or more observers create serialized copies of that object. These copies might be stored in a database, on a remote host, or in a local file, for example. Let's implement the core object using properties:

class Inventory:    def __init__(self):        self.observers = []        self._product = None        self._quantity = 0    def attach(self, observer):        self.observers.append(observer)    @property    def product(self):        return self._product    @product.setter    def product(self, value):        self._product = value        self._update_observers()    @property    def quantity(self):        return self._quantity    @quantity.setter def quantity(self, ...