1,利用委托替代继承
class Player:
def attack(self, x):
print('Player attack: ', x)
class Damage:
def __init__(self):
self._player = Player()
def damage(self, x):
print("damage: ", x)
self._player.attack(x)
def __getattr__(self, name):
return getattr(self._player, name)
d = Damage()
d.damage(100)
out:
damage: 100
Player attack: 100
2,定义多个构造函数
class Student:
def __init__(self, name, age):
self.name = name
self.age = age
@classmethod # 类方法
def Monitor(cls): #cls通常用作类方法的第一参数。通常用self来传递当前类对象的实例,cls传递当前类对象
return cls("Admin", 100)
def __str__(self):
return 'Student: ({!s})'.format(self.name)
a = Student('Leon', 66)
print(a)
print(Student.Monitor())
out:
Student: (Leon)
Student: (Admin)
2,状态机
class LightState: # 状态基类
@staticmethod
def turn_on(light):
raise NotImplementedError()
@staticmethod
def turn_off(light):
raise NotImplementedError()
@staticmethod
def do_work(light):
raise NotImplementedError()
class LightOnState: # 关灯状态,可以进行打开操作
@staticmethod
def turn_on(light):
raise RuntimeError('Already on')
@staticmethod
def turn_off(light):
light.new_state(LightOffState) # 将灯打开
@staticmethod
def do_work(light):
print('The light is on, just do it !!!')
class LightOffState: # 灯亮状态,可以进行工作和关灯操作
@staticmethod
def turn_on(light):
light.new_state(LightOnState)
@staticmethod
def turn_off(light):
raise RuntimeError('Already off')
@staticmethod
def do_work(light):
raise RuntimeError('light is not on')
class Light:
def __init__(self):
self.new_state(LightOffState) # 初始化状态
def new_state(self, newstate): # 更改状态
self._state = newstate # 委托操作,将特定操作交给另一个对象实现
def turn_on(self): # 委托代理操作
return self._state.turn_on(self)
def turn_off(self):
return self._state.turn_off(self)
def do_work(self):
return self._state.do_work(self)
l = Light()
print(l._state)
l.turn_on()
l.do_work()
l.turn_off()
l.do_work()
out:
<class '__main__.LightOffState'>
The light is on, just do it !!!
Traceback (most recent call last):...
RuntimeError: light is not on
另一种实现时直接修改实例的__class__属性
class Light: # 基类
def __init__(self):
self.new_state(LightOffState)
def new_state(self, newstate):
self.__class__ = newstate # 直接更改__class__属性
def turn_on(self):
raise NotImplementedError()
def turn_off(self):
raise NotImplementedError()
def do_work(self):
raise NotImplementedError()
class LightOnState(Light): # 继承Light类
def turn_on(light):
raise RuntimeError('Already on')
def turn_off(light):
light.new_state(LightOffState)
def do_work(light):
print('The light is on, just do it !!!')
class LightOffState(Light):
def turn_on(light):
light.new_state(LightOnState)
def turn_off(light):
raise RuntimeError('Already off')
def do_work(light):
raise RuntimeError('light is not on')
l = Light()
l.turn_on()
l.do_work()
l.turn_off()
l.do_work()