类变量与对象变量

类变量与对象变量

代码

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# coding=UTF-8,类变量与对象变量
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 # 这是一个类变量,属于Robot类

def __init__(self, name): # name变量属于一个对象(通过self分配),因此它是一个对象变量
"""初始化数据"""
self.name = name
print("(Initializing {})".format(self.name))

# 当有人被创建时,机器人会增加人口数量
'''
除了 Robot.popluation ,我们还可以使用 self.__class__.population ,因为每个对象都通过
self.__class__ 属性来引用它的类。
'''
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,你做得到"""
print("Greetings , my masters call me {}".format(self.name))

'''
classmethod 修饰符对应的函数不需要实例化,不需要 self 参数,
但第一个参数需要是表示自身类的 cls 参数,可以来调用类的属性,类的方法,实例化对象等。
'''

# how_many实际上是一个属于类而非属于对象的方法
# classmethod(类方法)或是一个staticmethod(静态方法)
@classmethod # 装饰器,等价于how_many = classmethod(how_many)
def how_many(cls):
"""打印出当前的人口数量"""
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()

运行结果

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(Initializing R2-D2)
Greetings , my masters call me R2-D2
We have 1 robots.
(Initializing C-3PO)
Greetings , my masters call me C-3PO
We have 2 robots.

Robots can do some work here.

Robots have finished their work. So let's destroy them.
R2-D2 is being destroyed!
There are still 1 robots working.
C-3PO is being destroyed!
C-3PO was the last one.
We have 0 robots.
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