Software Público Brasileiro

# Singleton and Publisher-Subscriber design patterns example.

from pubsub import pub as Publisher

class Singleton(type):
    # This is a Gary Robinson implementation:
    # http://www.garyrobinson.net/2004/03/python_singleto.html
    
    def __init__(cls,name,bases,dic):
        super(Singleton,cls).__init__(name,bases,dic)
        cls.instance=None
        
    def __call__(cls,*args,**kw):
        if cls.instance is None:
            cls.instance=super(Singleton,cls).__call__(*args,**kw)
        return cls.instance

class Pizza(object):
    # Only one project will be initialized per time. Therefore, we use
    # Singleton design pattern for implementing it
    __metaclass__= Singleton
    
    def __init__(self):
        self.npieces = 8
        self.__bind_events()
        
    def __bind_events(self):
        ps.Publisher().subscribe(self.RemovePiece,
                                 'Eat piece of pizza')
        
    def RemovePiece(self, pubsub_evt):
        person = pubsub_evt.data
        if self.npieces:
            self.npieces -= 1
            print "%s ate pizza!"%(person.name)
        else:
            print "%s is hungry!"%(person.name)

class Person():
    def __init__(self, name):
        self.name = name
        self.pizza = Pizza()
        
    def EatPieceOfPizza(self):
        ps.Publisher.sendMessage('Eat piece of pizza',(self))
        

print "Initial state:"
p1 = Person("Paulo ") 
p2 = Person("Thiago")
p3 = Person("Andre ")
people = [p1, p2, p3]

print "Everyone eats 2 pieces:"
for i in range(2):
    for person in people:
        person.EatPieceOfPizza()
    
print "Everyone tries to eat another piece:"
for person in people:
    person.EatPieceOfPizza()