class Robot: """Represents a robot, with a name.""" # A class variable, counting the number of robots population = 0 def __init__(self, name): """Initializes the data.""" self.name = name print("(Initializing {})".format(self.name)) # When this person is created, the robot # adds to the population Robot.population += 1 def die(self): """I am dying.""" print("{} is being destroyed!".format(self.name)) Robot.population -= 1 if Robot.population == 0: print("{} was the last one.".format(self.name)) else: print("There are still {:d} robots working.".format( Robot.population)) def say_hi(self): """Greeting by the robot. Yeah, they can do that.""" print("Greetings, my masters call me {}.".format(self.name)) @classmethod def how_many(cls): """Prints the current population.""" print("We have {:d} robots.".format(cls.population)) droid1 = Robot("R2-D2") droid1.say_hi() Robot.how_many() droid2 = Robot("C-3PO") droid2.say_hi() Robot.how_many() print("\nRobots can do some work here.\n") print("Robots have finished their work. So let's destroy them.") droid1.die() droid2.die() Robot.how_many()