Python实现简单状态框架的方法

本文实例讲述了Python实现简单状态框架的方法。分享给大家供大家参考。具体分析如下：

这里使用Python实现一个简单的状态框架，代码需要在python3.2环境下运行

from time import sleep

from random import randint, shuffle

class StateMachine(object):

    ''' Usage:  Create an instance of StateMachine, use set_starting_state(state) to give it an

        initial state to work with, then call tick() on each second (or whatever your desired

        time interval might be. '''

    def set_starting_state(self, state):

        ''' The entry state for the state machine. '''

        state.enter()

        self.state = state

    def tick(self):

        ''' Calls the current state's do_work() and checks for a transition '''

        next_state = self.state.check_transitions()

        if next_state is None:

            # Stick with this state

            self.state.do_work()

        else:

            # Next state found, transition to it

            self.state.exit()

            next_state.enter()

            self.state = next_state

class BaseState(object):

    ''' Usage: Subclass BaseState and override the enter(), do_work(), and exit() methods.

            enter()    -- Setup for your state should occur here.  This likely includes adding

                          transitions or initializing member variables.

            do_work()  -- Meat and potatoes of your state.  There may be some logic here that will

                          cause a transition to trigger.

            exit()     -- Any cleanup or final actions should occur here.  This is called just

                          before transition to the next state.

    '''

    def add_transition(self, condition, next_state):

        ''' Adds a new transition to the state.  The "condition" param must contain a callable

            object.  When the "condition" evaluates to True, the "next_state" param is set as

            the active state. '''

        # Enforce transition validity

        assert(callable(condition))

        assert(hasattr(next_state, "enter"))

        assert(callable(next_state.enter))

        assert(hasattr(next_state, "do_work"))

        assert(callable(next_state.do_work))

        assert(hasattr(next_state, "exit"))

        assert(callable(next_state.exit))

        # Add transition

        if not hasattr(self, "transitions"):

            self.transitions = []

        self.transitions.append((condition, next_state))

    def check_transitions(self):

        ''' Returns the first State thats condition evaluates true (condition order is randomized) '''

        if hasattr(self, "transitions"):

            shuffle(self.transitions)

            for transition in self.transitions:

                condition, state = transition

                if condition():

                    return state

    def enter(self):

        pass

    def do_work(self):

        pass

    def exit(self):

        pass

##################################################################################################

############################### EXAMPLE USAGE OF STATE MACHINE ###################################

##################################################################################################

class WalkingState(BaseState):

    def enter(self):

        print("WalkingState: enter()")

        def condition(): return randint(1, 5) == 5

        self.add_transition(condition, JoggingState())

        self.add_transition(condition, RunningState())

    def do_work(self):

        print("Walking...")

    def exit(self):

        print("WalkingState: exit()")

class JoggingState(BaseState):

    def enter(self):

        print("JoggingState: enter()")

        self.stamina = randint(5, 15)

        def condition(): return self.stamina <= 0

        self.add_transition(condition, WalkingState())

    def do_work(self):

        self.stamina -= 1

        print("Jogging ({0})...".format(self.stamina))

    def exit(self):

        print("JoggingState: exit()")

class RunningState(BaseState):

    def enter(self):

        print("RunningState: enter()")

        self.stamina = randint(5, 15)

        def walk_condition(): return self.stamina <= 0

        self.add_transition(walk_condition, WalkingState())

        def trip_condition(): return randint(1, 10) == 10

        self.add_transition(trip_condition, TrippingState())

    def do_work(self):

        self.stamina -= 2

        print("Running ({0})...".format(self.stamina))

    def exit(self):

        print("RunningState: exit()")

class TrippingState(BaseState):

    def enter(self):

        print("TrippingState: enter()")

        self.tripped = False

        def condition(): return self.tripped

        self.add_transition(condition, WalkingState())

    def do_work(self):

        print("Tripped!")

        self.tripped = True

    def exit(self):

        print("TrippingState: exit()")

if __name__ == "__main__":

    state = WalkingState()

    state_machine = StateMachine()

    state_machine.set_starting_state(state)

    while True:

        state_machine.tick()

        sleep(1)

希望本文所述对大家的Python程序设计有所帮助。