关键错误：Python 有限状态机？

Question

这是我在 Python 中简单实现有限状态机的代码。我已经多次运行它无济于事。当各个状态类确实从各个类继承时，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。我该如何解决这个错误？有没有更好/正确的方法来组织我的课程？我在 python 方面处于中级水平，但是 OOP 概念对我来说尤其具有挑战性。任何帮助和建议将不胜感激！

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

这里的问题是您在执行更新时引用了不同的 fsm 对象。

在execute 代码 sn-p 中，当您更新状态时，问题是虽然单个对象存在 FSM 对象，但 eat 类不存在它，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，因此如果您想对属于单个类的FSM 对象进行操作，您需要将个体作为输入传递。

也就是说，这里的eat 块真的不应该是一个类，而应该是individual 的一个函数，而不是从它继承。例如：

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。

我认为您总体上对 OOP 有一些困惑。继承根本不与特定对象实例交互。相反，这就像说：“我需要创建一个新对象，但让我将这个旧对象用作模板并添加到它”。

您在这里尝试做的更接近于创建单例，这是一个具有在其他地方引用的单一状态的对象。并非一切都应该是一个对象。例如，处理程序通常是函数，依靠魔术execute 函数而不是仅仅执行函数是相当迂回的。

Answer 2

正如 Slater Tyranus 所提到的，问题在于您正在创建 individual 的状态（wander、eat 和 sleep 类）子类。这是不正确的。将子类化视为说某事“是”另一件事。例如，对于类声明class Car(Vehicle):，您实质上是在说“Car 是Vehicle”，这是一个真实的陈述。但是，您的代码暗示 wander 状态是个人，这是不正确的。另一个问题是，因为每个州都是独立的，所以每个州都有自己的 fsm。这不是必需的，个人也不应该首先拥有 fsm（你有吗？我没有）。

我已经重构了您的代码，并简化了状态中的条件，更正了过程中的一些其他错误。看看这是否更符合您的预期：

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()