Python实现简单状态框架的方法

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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

复制代码代码如下:

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 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 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))

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