class Robot:
	"""表示有一个带有名字的机器人"""

	#一个类变量，用来计数机器人的数量
	population = 0

	def __init__(self,name):
		"""初始化数据"""
		self.name = name
		print("(Initializing {})".format(self.name))


		#当有人创建时，机器人数量+1
		Robot.population += 1

	def die(self):
		"""我挂了"""
		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):
		"""来自机器人的诚挚问候

		没问题，你做的到"""
		print("Greetings,my masters call me {}".format(self.name))

	@classmethod
	def how_many(cls):
		"""打印出当前的数量"""
		print("We have {:d} robots.".format(cls.population))

droid1 = Robot("R2-D2")
droid1.say_hi()
Robot.how_many()

droid2 = Robot('J-11')
droid2.say_hi()
droid2.how_many()

print("\nRobots can do some work her.\n")

print("Robots have finished their work. So let's destroy them.")
droid1.die()
droid2.die()

Robot.how_many()

print(Robot.__doc__)
print(Robot.say_hi.__doc__)