Let's Learn Python #19 - Finite-State Machines (FSM)

This week, I cover what a Finite-State Machine (FSM) is, how to plan one out, how to create two different ones and why we use them!

LINK TO AI BOOK:

Please leave me a comment or question below! Like and Subscribe to show your support! :D

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Music by Juto: Link Coming Soon!

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--- SUPER TUTORIAL LIST!!! ---

PLAYLISTS

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[pinch-of-salt]

I love your videos!! I love these advanced programming concepts unlike the other tutorials that keep going on about loops and stuff. Make a python 3 version of these and add more things please! Thank you!

[mag]

This is an excellent tutorial. I had to watch the whole thing about 3 times but was able to use your method to create my own functioning FSM in about an hour. I appreciate it!

[VeronikaAlexander]

Thanks for this video! I have your book, but the link to the source code leads to nowhere... Is there another place where I can download the scripts?

[californiaesnuestra]

In the second example you need to initialize the current state for the RobotMaid, example: r.FSM.SetState("Sleep"), otherwise you will get: AttributeError: 'NoneType' object has no attribute 'Execute'

[bluegiger]

Hey Trevor, I like your video. I have a small bit of feedback: For your actual code, you might find that using a monospaced font makes it easier to read.

[steampunk]

well that's a clear and not so long way to explain how to implement a FSM.
thanks a lot

[vzuzukin]

I like your series on Python.  This and another called "Python By Osmosis" are the most informative nuggets of Python I've found on YouTube broken down in 5-10 minute bytes.  Would you be interested in doing some videos on Rasberry Pi DIY projects in Python?

[billma]

Hi, thank you for the video. Where can we find the files/codes in the video? Thanks

[RobbieNerve]

Thanks for creating this! It helped me understand the concept better. cheers!

[PrathamGupta]

Can you please share the code you used in the example, please?

[torylva]

Hello! Thanks for an really nice tutorial, but I have one question (If you see this)

If I would want to have multiple robot maids with unique IDs (As in the book "Programming Game AI by Example"), should I make the Char an actual class and have it produce A unique ID for each?
Or should I simply make a Dictionary in the main function that stores each object with a unique ID assigned as the Key?

Which would you recommend?

[sofianfadli]

Hey, Trevor. I want to ask. Why I just showing "Transitioning..." when I run the code. Where i had created mistakes. Thank you very much
from random import randint
from time import clock


State = type("State", (object, ), {})

class LightOn(State):
def Execute(self):
print ("Light is On!")

class LightOff(State):
def Execute(self):
print ("Light is Off!")



class Transition(object):
def __init__(self, toState):
self.toState = toState

def Execute(self):
print ("Transitioning...")




class SimpleFSM(object):
def __init__(self, char):
self.char = char
self.states = {}
self.transitions = {}
self.curState = None
self.trans = None

def SetState(self, stateName):
self.curState = self.states[stateName]

def Transition(self, transName):
self.trans = self.transitions[transName]

def Execute(self):
if (self.trans):
self.trans.Execute()

self.trans = None
self.curState.Execute



class Char(object):
def __init__(self):
self.FSM = SimpleFSM(self)
self.LightOn = True



if __name__ == "__main__":
light = Char()

light.FSM.states["On"] = LightOn()
light.FSM.states["Off"] = LightOff()
light.FSM.transitions["toOn"] = Transition("On")
= Transition("Off")

light.FSM.SetState("On")

for i in range(20):
startTime = clock()
timeInterval = 1
while (startTime + timeInterval > clock()):
pass
if (randint(0, 2)):
if (light.LightOn):
light.FSM.Transition("toOff")
light.LightOn = False
else:
light.FSM.Transition("toOn")
light.LightOn = True
light.FSM.Execute()

[dsdsdsds]

this video was really helpful. thank you!

[daydreamer]

Lovely tutorial Man!!
Can we use customised ContextManagers for enter and exit states?

[abhinabmohanty]

Hi Trevor, Thanks for this video it was really helpful. As i am building a FSM for one of my projects...
I tried implementing the code but i keep getting this error: self.FSM.AddState("Sleep", Sleep(self.FSM))
AttributeError: 'FSM' object has no attribute 'AddState'

i checked for spelling but everything seems fine. Could you help please?

[danielchan]

it is a great idea of F.S.M. I had try the codes of robotfsm.py In raspberrypi. it works good, but fail some times after running for five or ten seconds. do you have any idea to fix it? I had checked with the video carefully with/nothing wrong. Thankyou your tutorial!

[fuhodev]

thank you very much, your tutorial is very helpful

[thestarseekers]

Is it possible for us to see the full source code? I keep on comparing your lightbulb FSM to the one I made, and keep on running into this error: 

Traceback (most recent call last):
  File Learn\lightbulb_FSM.py", line 76, in <module>
    light.FSM.Transition("toOn")
  File Learn\lightbulb_FSM.py", line 38, in Transition
    self.trans = self.transitions[transName]
KeyError: 'toOn'

Is it just a Python 3.x problem, or is it just a problem in my program? 

[alexandrumarianlita]

If I have a complex game and I have there for example state for menu, for play, for exit, etc. I need to create a different state machine to handle player states and a different state machine to handle menu state and other things? A game event in a MMORPG can be a state to? 

[AnuragBisht]

Amazing tutorial like your series :)
just one thing though in actual state e.g. CleanDishes you don't need __init__.