Key Error: Python Finite State Machine?

Question

这是我在 Python 中简单实现有限状态机的代码。我有运行多次都无济于事。当个体状态 classes 确实继承自个体 class 时，它们无法访问运行机器逻辑所需的食物和睡眠变量。我相信我遇到了 KeyError，因为每次我添加新状态时，它都会将当前状态值重置为 None。我怎样才能解决这个错误？是否有 better/proper 方法来构建我的 classes？我处于 python 的中级水平，但是 OOP 概念对我来说特别具有挑战性。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指的是不同的 fsm 对象。

在 execute 代码片段中，当您更新状态时，问题是虽然 FSM 对象存在于单个对象中，但它不存在于 eat 中class，你尝试更新 eat class.

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classes共享一个FSM实例，所以如果你想对属于个体class的FSM对象进行操作] 您需要将个人作为输入传递。

也就是说，这里的eat块真的不应该是class，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 实际上指的是 individual 对象。

我认为您一般对 OOP 有一些困惑。继承根本不与特定对象实例交互。相反，它就像在说："I need to make a new object, but let me use this old one as a template and just add to it".

您在这里尝试做的事情更接近于创建单例，单例是一个对象，具有在别处引用的单一状态。并非所有东西都应该是对象。例如，处理程序通常是函数，依赖魔法 execute 函数而不是仅仅执行函数是相当迂回的。

Answer 2

正如 Slater Tyranus 提到的，问题是您正在使状态 (wander、eat 和 sleep classes) subclass individual 的 es。这是不正确的。把 subclassing 想成是在说 "is" 别的东西。例如，使用 class 声明 class Car(Vehicle):，您实际上是在说 "a Car is a Vehicle"，这是一个正确的陈述。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状态都是一个个体，每个状态都有自己的 fsm。这不是必需的，个人也不应该首先拥有 fsm（你有吗？我没有）。

我重构了你的代码，简化了状态中的条件，更正了过程中的其他一些错误。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()

Key Error: Python Finite State Machine?

Key Error: Python Finite State Machine?

python

oop

fsm