class StateMachine:
    def __init__(self):
        self.handlers = {}  # 状态转移函数字典
        self.startState = None  # 初始状态
        self.endState = []  # 最终状态集合

    # 参数name为状态名,handler为状态转移函数,end_state表明是否为最终状态
    def add_state(self, name, handler, end_state=0):
        name = name.upper()
        self.handlers[name] = handler
        if end_state:
            self.endState.append(name)

    def set_start(self, name):
        self.startState = name.upper()

    def run(self, cargo):
        try:
            handler = self.handlers[self.startState]
        except:
            raise Exception("must call .set_start() before .run()")
        if not self.endState:
            raise Exception("at least one state must be an end_state")

        while True:
            (newState, cargo) = handler(cargo)
            if newState.upper() in self.endState:
                print("reached ", newState)
                break
            else:
                handler = self.handlers[newState.upper()]


# 有限状态集合
positive_adjectives = ["great", "super", "fun", "entertaining", "easy"]
negative_adjectives = ["boring", "difficult", "ugly", "bad"]


# 自定义状态转变函数
def start_transitions(txt):
    # 用指定分隔符对字符串进行切片,默认为空格分割,参数num指定分割次数
    # 将"Python is XXX"语句分割为"Python"和之后的"is XXX"
    splitted_txt = txt.split(None, 1)
    word, txt = splitted_txt if len(splitted_txt) > 1 else (txt, "")
    if word == "Python":
        newState = "Python_state"  # 如果第一个词是Python则可转换到"Python状态"
    else:
        newState = "error_state"  # 如果第一个词不是Python则进入终止状态
    return (newState, txt)  # 返回新状态和余下的语句txt


def python_state_transitions(txt):
    splitted_txt = txt.split(None, 1)
    word, txt = splitted_txt if len(splitted_txt) > 1 else (txt, "")
    if word == "is":
        newState = "is_state"
    else:
        newState = "error_state"
    return (newState, txt)


def is_state_transitions(txt):
    splitted_txt = txt.split(None, 1)
    word, txt = splitted_txt if len(splitted_txt) > 1 else (txt, "")
    if word == "not":
        newState = "not_state"
    elif word in positive_adjectives:
        newState = "pos_state"
    elif word in negative_adjectives:
        newState = "neg_state"
    else:
        newState = "error_state"
    return (newState, txt)


def not_state_transitions(txt):
    splitted_txt = txt.split(None, 1)
    word, txt = splitted_txt if len(splitted_txt) > 1 else (txt, "")
    if word in positive_adjectives:
        newState = "neg_state"
    elif word in negative_adjectives:
        newState = "pos_state"
    else:
        newState = "error_state"
    return (newState, txt)


if __name__ == "__main__":
    m = StateMachine()
    m.add_state("Start", start_transitions)  # 添加初始状态
    m.add_state("Python_state", python_state_transitions)
    m.add_state("is_state", is_state_transitions)
    m.add_state("not_state", not_state_transitions)
    m.add_state("neg_state", None, end_state=1)  # 添加最终状态
    m.add_state("pos_state", None, end_state=1)
    m.add_state("error_state", None, end_state=1)

    m.set_start("Start")  # 设置开始状态
    m.run("Python is great")
    m.run("Python is not fun")
    m.run("Perl is ugly")
    m.run("Pythoniseasy")

摘自 有限状态机(Python)