class ObserverPattern(object):
    """Demonstrates the observer pattern."""

    def __init__(self):
        self.nora = Human("Nora")
        self.cat = Cat("Mona")
        self.nora.adopt_cat(self.cat)

    def demonstrate(self):
        self.cat.be_a_cat()
 def __init__(self):
     self.nora = Human("Nora")
     self.cat = Cat("Mona")
     self.nora.adopt_cat(self.cat)