关键错误:Python有限状态机

Question

以下是我在Python中简单实现有限状态机的代码。我已经运行了多次，但都没有用。当单个状态类从单个类继承时，它们无法访问运行机器逻辑所需的食物和睡眠变量。我相信我得到了一个KeyError，因为每次我添加一个新状态时，它都会将"当前状态值"重置为"无"。我该如何避免这个错误？有没有更好/合适的方法来组织我的课程？我是python的中级，但是OOP概念对我来说特别有挑战性。任何帮助和建议都将不胜感激！

class FSM():
    def __init__(self):
        self.states = {}
        self.c_state = None
    def update(self):
        self.states[self.c_state].execute()
    def addState(self, name, handler):
        self.states[name] = handler
    def startState(self, state):
        self.c_state = state
    def changeState(self, newstate):
        print('The current state is:', self.c_state)
        self.states[self.c_state].exit()
        self.c_state = self.states[newstate]
        self.states[self.c_state].enter()
class individual():
    def __init__(self, name, food, sleep):
        self.name = name
        self.food = food
        self.sleep = sleep
        self.fsm = FSM()
class wander(individual):
    def enter(self):
        print('Entering Wander State')
    def execute(self):
        print('WANDERING')
        if self.sleep == 0:
            self.fsm.changeState('SLEEP')
        elif 25 > self.sleep > 0 and self.food > 25:
            self.fsm.changeState('WANDER')
            self.sleep -= 5
            self.food -= 5
        elif self.food < 25:
            self.fsm.changeState('EAT')
    def exit(self):
        print('Leaving Wander State')
class eat(individual):
    def enter(self):
        print('Entering Eating State')
    def execute(self):
        print('EATING')
        if self.sleep > 0 and self.food < 25:
            self.fsm.changeState('EAT')
            self.food += 5
            self.sleep -= 5
        elif self.food > 25 and self.sleep > 0:
            self.fsm.changeState('WANDER')
        elif self.sleep == 0:
            self.fsm.changeState('SLEEP')
    def exit(self):
        print('Exiting Eating State')
class sleep(individual):
    def enter(self):
        print('Entering Sleeping State')
    def execute(self):
        print('SLEEPING')
        if 50 > self.sleep > 0:
            self.fsm.changeState('SLEEP')
            self.sleep += 5
        elif self.sleep == 50 and self.food < 25:
            self.fsm.changeState('EAT')
        elif self.sleep == 50 and self.food > 25:
            self.fsm.changeState('WANDER')
    def exit(self):
        print('Exiting Sleeping State')
aaron = individual('aaron', 10, 30)
aaron.fsm.addState('WANDER', wander(aaron.name, aaron.food, aaron.sleep))
aaron.fsm.addState('EAT', eat(aaron.name, aaron.food, aaron.sleep))
aaron.fsm.addState('SLEEP', sleep(aaron.name, aaron.food, aaron.sleep))
aaron.fsm.startState('WANDER')
print(aaron.fsm.c_state)
aaron.fsm.update()
 File "C:/Users/Aaron/PycharmProjects/InDepthFSM/FSM.py", line 12, in update
    self.states[self.c_state].execute()
  File "C:/Users/Aaron/PycharmProjects/InDepthFSM/FSM.py", line 50, in execute
    self.fsm.changeState('EAT')
  File "C:/Users/Aaron/PycharmProjects/InDepthFSM/FSM.py", line 24, in changeState
    self.states[self.c_state].exit()
KeyError: None

Answer 1

这里的问题是在执行更新时引用了不同的fsm对象。

在execute代码段中，当您更新状态时，问题是虽然FSM对象对于单个对象存在，但对于eat类不存在，并且您尝试更新eat类的状态。

# Here, since self refers to the `eat` class, you are creating a new fsm object
# This means that you are in fact referring to an empty set of states.
elif self.sleep == 0:
   self.fsm.changeState('SLEEP')

继承并不意味着类共享一个FSM实例，因此，如果要对属于单个类的FSM对象进行操作，则需要将该对象作为输入进行传递。

也就是说，这里的eat片段实际上不应该是一个类，而应该是individual的一个函数，而不是从它继承

class individual(object):
    def __init__(self, ...):
        # make object
    def eat(self):
        print('EATING')
        if self.sleep > 0 and self.food < 25:
            self.fsm.changeState('EAT')
            self.food += 5
            self.sleep -= 5
        elif self.food > 25 and self.sleep > 0:
            self.fsm.changeState('WANDER')
        elif self.sleep == 0:
            self.fsm.changeState('SLEEP')

在这种情况下，self实际上是指individual对象。

我想你对OOP总的来说有些困惑。继承根本不与特定的对象实例交互。相反，这就像是在说："我需要制作一个新对象，但让我用这个旧对象作为模板，然后添加到它中"。

您在这里尝试做的是更接近于创建一个singleton，它是一个具有在其他地方引用的单个状态的对象。并不是所有的东西都应该是一个物体。例如，处理程序通常是函数，依赖一个神奇的execute函数而不仅仅是执行一个函数是非常迂回的。

Answer 2

正如Slater Tyranus所提到的，问题是您正在使状态（wander、eat和sleep类）成为individual的子类。这是不对的。把子类化看作是说某个东西"是"另一个东西。例如，使用类声明class Car(Vehicle):，您实际上是在说"Car就是Vehicle"，这是一个真实的语句。但是，您的代码暗示wander状态是一个个体，这不是真的。另一个问题是，因为每个状态都是单独的，所以每个状态都有自己的fsm。这不是必要的，个人也不应该首先拥有fsm（你有吗？我没有）。

我重构了您的代码，简化了状态中的条件，纠正了过程中的其他一些错误。看看这是否更符合你的预期：

class FSM(object):
    def __init__(self, individual):
        self.states = {}
        self.c_state = None
        self.individual = individual
    def update(self):
        self.states[self.c_state].execute(self)
    def addState(self, name, handler):
        self.states[name] = handler
    def startState(self, state):
        self.c_state = state
    def changeState(self, newstate):
        print('The current state is:', self.c_state)
        self.states[self.c_state].exit()
        self.c_state = newstate
        self.states[self.c_state].enter()

class Individual(object):
    def __init__(self, name, food, sleep):
        self.name = name
        self.food = food
        self.sleep = sleep

class Wander():
    @staticmethod
    def enter():
        print('Entering Wander State')
    @staticmethod
    def execute(fsm):
        print('WANDERING')
        if fsm.individual.sleep <= 0:
            fsm.changeState('SLEEP')
        elif fsm.individual.food >= 25:
            fsm.changeState('WANDER')
            fsm.individual.sleep -= 5
            fsm.individual.food -= 5
        else:
            fsm.changeState('EAT')
    @staticmethod
    def exit():
        print('Leaving Wander State')

class Eat():
    @staticmethod
    def enter():
        print('Entering Eating State')
    @staticmethod
    def execute(fsm):
        print('EATING')
        if fsm.individual.sleep <= 0:
            fsm.changeState('SLEEP')
        elif fsm.individual.food < 25:
            fsm.changeState('EAT')
            fsm.individual.food += 5
            fsm.individual.sleep -= 5
        else:
            fsm.changeState('WANDER')
    @staticmethod
    def exit():
        print('Exiting Eating State')

class Sleep():
    @staticmethod
    def enter():
        print('Entering Sleeping State')
    @staticmethod
    def execute(fsm):
        print('SLEEPING')
        if fsm.individual.sleep < 50:
            fsm.changeState('SLEEP')
            fsm.individual.sleep += 5
        elif fsm.individual.food < 25:
            fsm.changeState('EAT')
        else:
            fsm.changeState('WANDER')
    @staticmethod
    def exit():
        print('Exiting Sleeping State')
aaron = Individual('aaron', 10, 30)
fsm = FSM(aaron)
fsm.addState('WANDER', Wander)
fsm.addState('EAT', Eat)
fsm.addState('SLEEP', Sleep)
fsm.startState('WANDER')
print(fsm.c_state)
fsm.update()