http://eyehere.net/2011/python-pygame-novice-professional-index/

FSM(Finite-state machine)的严格定义，需要state和action和转移函数都是确定性的，也就是说，必须要在完全把握所有交互可能性的时候，限定一个有限的交互状态、交互动作和转移函数。

使用场景: 根据上面的定义就可以知道FSM在使用前必须已经确定了所有的状态,所有的状态转移情况

可以这样简单的理解生活中但凡有流程性质的东西都可以使用状态机来处理

class State(object):
    def __init__(self, name):
        self.name = name
    def do_actions(self):
        pass

    def check_conditions(self):
        pass

    def entry_actions(self):
        pass

    def exit_actions(self):
        pass


class StateMachine(object):
    def __init__(self):
        self.states = {}
        self.active_state = None

    def add_state(self, state):
        self.states[state.name] = state

    def main_task(self):
        if self.active_state is None:
            return
        self.active_state.do_actions()
        new_state_name = self.active_state.check_conditions()
        if new_state_name is not None:
            self.set_state(new_state_name)

    def set_state(self, new_state_name):
        if self.active_state is not None:
            self.active_state.exit_actions()
        self.active_state = self.states[new_state_name]
        self.active_state.entry_actions()

上面是状态机抽象模型
懒得写 直接看别人写好的吧.(上面链接教程 index_16)

SCREEN_SIZE = (640, 480)
NEST_POSITION = (320, 240)
ANT_COUNT = 20
NEST_SIZE = 100.
 
import pygame
from pygame.locals import *
 
from random import randint, choice
from gameobjects.vector2 import Vector2
 
class State(object):
    def __init__(self, name):
        self.name = name
    def do_actions(self):
        pass
    def check_conditions(self):
        pass
    def entry_actions(self):
        pass
    def exit_actions(self):
        pass        
 
class StateMachine(object):
    def __init__(self):
        self.states = {}
        self.active_state = None
 
    def add_state(self, state):
        self.states[state.name] = state
 
    def think(self):
        if self.active_state is None:
            return
        self.active_state.do_actions()
        new_state_name = self.active_state.check_conditions()
        if new_state_name is not None:
            self.set_state(new_state_name)
 
    def set_state(self, new_state_name):
        if self.active_state is not None:
            self.active_state.exit_actions()
        self.active_state = self.states[new_state_name]
        self.active_state.entry_actions()
 
class World(object):
    def __init__(self):
        self.entities = {}
        self.entity_id = 0
        self.background = pygame.surface.Surface(SCREEN_SIZE).convert()
        self.background.fill((255, 255, 255))
        pygame.draw.circle(self.background, (200, 255, 200), NEST_POSITION, int(NEST_SIZE))
 
    def add_entity(self, entity):
        self.entities[self.entity_id] = entity
        entity.id = self.entity_id
        self.entity_id += 1
 
    def remove_entity(self, entity):
        del self.entities[entity.id]
 
    def get(self, entity_id):
        if entity_id in self.entities:
            return self.entities[entity_id]
        else:
            return None
 
    def process(self, time_passed):
        time_passed_seconds = time_passed / 1000.0
        for entity in self.entities.values():
            entity.process(time_passed_seconds)
 
    def render(self, surface):
        surface.blit(self.background, (0, 0))
        for entity in self.entities.itervalues():
            entity.render(surface)
 
    def get_close_entity(self, name, location, range=100.):
        location = Vector2(*location)
        for entity in self.entities.itervalues():
            if entity.name == name:
                distance = location.get_distance_to(entity.location)
                if distance < range:
                    return entity
        return None
 
class GameEntity(object):
 
    def __init__(self, world, name, image):
 
        self.world = world
        self.name = name
        self.image = image
        self.location = Vector2(0, 0)
        self.destination = Vector2(0, 0)
        self.speed = 0.
        self.brain = StateMachine()
        self.id = 0
 
    def render(self, surface):
        x, y = self.location
        w, h = self.image.get_size()
        surface.blit(self.image, (x-w/2, y-h/2))   
 
    def process(self, time_passed):
        self.brain.think()
        if self.speed > 0. and self.location != self.destination:
            vec_to_destination = self.destination - self.location
            distance_to_destination = vec_to_destination.get_length()
            heading = vec_to_destination.get_normalized()
            travel_distance = min(distance_to_destination, time_passed * self.speed)
            self.location += travel_distance * heading
 
class Leaf(GameEntity):
    def __init__(self, world, image):
        GameEntity.__init__(self, world, "leaf", image)
 
class Spider(GameEntity):
    def __init__(self, world, image):
        GameEntity.__init__(self, world, "spider", image)
        self.dead_image = pygame.transform.flip(image, 0, 1)
        self.health = 25
        self.speed = 50. + randint(-20, 20)
 
    def bitten(self):
        self.health -= 1
        if self.health <= 0:
            self.speed = 0.
            self.image = self.dead_image
        self.speed = 140.
 
    def render(self, surface):
        GameEntity.render(self, surface)
        x, y = self.location
        w, h = self.image.get_size()
        bar_x = x - 12
        bar_y = y + h/2
        surface.fill( (255, 0, 0), (bar_x, bar_y, 25, 4))
        surface.fill( (0, 255, 0), (bar_x, bar_y, self.health, 4))
 
    def process(self, time_passed):
        x, y = self.location
        if x > SCREEN_SIZE[0] + 2:
            self.world.remove_entity(self)
            return
        GameEntity.process(self, time_passed)
 
class Ant(GameEntity):
    def __init__(self, world, image):
        GameEntity.__init__(self, world, "ant", image)
        exploring_state = AntStateExploring(self)
        seeking_state = AntStateSeeking(self)
        delivering_state = AntStateDelivering(self)
        hunting_state = AntStateHunting(self)
        self.brain.add_state(exploring_state)
        self.brain.add_state(seeking_state)
        self.brain.add_state(delivering_state)
        self.brain.add_state(hunting_state)
        self.carry_image = None
 
    def carry(self, image):
        self.carry_image = image
 
    def drop(self, surface):
        if self.carry_image:
            x, y = self.location
            w, h = self.carry_image.get_size()
            surface.blit(self.carry_image, (x-w, y-h/2))
            self.carry_image = None
 
    def render(self, surface):
        GameEntity.render(self, surface)
        if self.carry_image:
            x, y = self.location
            w, h = self.carry_image.get_size()
            surface.blit(self.carry_image, (x-w, y-h/2))
 
class AntStateExploring(State):
    def __init__(self, ant):
        State.__init__(self, "exploring")
        self.ant = ant
 
    def random_destination(self):
        w, h = SCREEN_SIZE
        self.ant.destination = Vector2(randint(0, w), randint(0, h))    
 
    def do_actions(self):
        if randint(1, 20) == 1:
            self.random_destination()
 
    def check_conditions(self):
        leaf = self.ant.world.get_close_entity("leaf", self.ant.location)
        if leaf is not None:
            self.ant.leaf_id = leaf.id
            return "seeking"
        spider = self.ant.world.get_close_entity("spider", NEST_POSITION, NEST_SIZE)
        if spider is not None:
            if self.ant.location.get_distance_to(spider.location) < 100.:
                self.ant.spider_id = spider.id
                return "hunting"
        return None
 
    def entry_actions(self):
        self.ant.speed = 120. + randint(-30, 30)
        self.random_destination()
 
class AntStateSeeking(State):
    def __init__(self, ant):
        State.__init__(self, "seeking")
        self.ant = ant
        self.leaf_id = None
 
    def check_conditions(self):
        leaf = self.ant.world.get(self.ant.leaf_id)
        if leaf is None:
            return "exploring"
        if self.ant.location.get_distance_to(leaf.location) < 5.0:
            self.ant.carry(leaf.image)
            self.ant.world.remove_entity(leaf)
            return "delivering"
        return None
 
    def entry_actions(self):
        leaf = self.ant.world.get(self.ant.leaf_id)
        if leaf is not None:
            self.ant.destination = leaf.location
            self.ant.speed = 160. + randint(-20, 20)
 
class AntStateDelivering(State):
    def __init__(self, ant):
        State.__init__(self, "delivering")
        self.ant = ant
 
    def check_conditions(self):
        if Vector2(*NEST_POSITION).get_distance_to(self.ant.location) < NEST_SIZE:
            if (randint(1, 10) == 1):
                self.ant.drop(self.ant.world.background)
                return "exploring"
        return None
 
    def entry_actions(self):
        self.ant.speed = 60.
        random_offset = Vector2(randint(-20, 20), randint(-20, 20))
        self.ant.destination = Vector2(*NEST_POSITION) + random_offset       
 
class AntStateHunting(State):
    def __init__(self, ant):
        State.__init__(self, "hunting")
        self.ant = ant
        self.got_kill = False
 
    def do_actions(self):
        spider = self.ant.world.get(self.ant.spider_id)
        if spider is None:
            return
        self.ant.destination = spider.location
        if self.ant.location.get_distance_to(spider.location) < 15.:
            if randint(1, 5) == 1:
                spider.bitten()
                if spider.health <= 0:
                    self.ant.carry(spider.image)
                    self.ant.world.remove_entity(spider)
                    self.got_kill = True
 
    def check_conditions(self):
        if self.got_kill:
            return "delivering"
        spider = self.ant.world.get(self.ant.spider_id)
        if spider is None:
            return "exploring"
        if spider.location.get_distance_to(NEST_POSITION) > NEST_SIZE * 3:
            return "exploring"
        return None
 
    def entry_actions(self):
        self.speed = 160. + randint(0, 50)
 
    def exit_actions(self):
        self.got_kill = False
 
def run():
    pygame.init()
    screen = pygame.display.set_mode(SCREEN_SIZE, 0, 32)
    world = World()
    w, h = SCREEN_SIZE
    clock = pygame.time.Clock()
    ant_image = pygame.image.load("ant.png").convert_alpha()
    leaf_image = pygame.image.load("leaf.png").convert_alpha()
    spider_image = pygame.image.load("spider.png").convert_alpha()
 
    for ant_no in xrange(ANT_COUNT):
        ant = Ant(world, ant_image)
        ant.location = Vector2(randint(0, w), randint(0, h))
        ant.brain.set_state("exploring")
        world.add_entity(ant)
 
    while True:
        for event in pygame.event.get():
            if event.type == QUIT:
                return
        time_passed = clock.tick(30)
 
        if randint(1, 10) == 1:
            leaf = Leaf(world, leaf_image)
            leaf.location = Vector2(randint(0, w), randint(0, h))
            world.add_entity(leaf)
 
        if randint(1, 100) == 1:
            spider = Spider(world, spider_image)
            spider.location = Vector2(-50, randint(0, h))
            spider.destination = Vector2(w+50, randint(0, h))
            world.add_entity(spider)
 
        world.process(time_passed)
        world.render(screen)
 
        pygame.display.update()
 
if __name__ == "__main__":
    run()