Can I set up a Finite-State Machine using Python?
I'm looking to input a string and have the program throw a boolean whereas True means the string is contained in the FSM.
>>55072898
>Can I set up a Finite-State Machine using Python?
You have to implement it, but yes.
>>55072898
FSMs are bad because they mutate state
The best program is one completely free of side-effects.
t. functional programmer
>>55072930
That's a strawman of how functional programmers advocate state and immutable logic.
>>55072930
Doesn't python have unchangeable states?
>>55072921
Ok, how? I know how to tell if a string is accepted IRL, i have no clue how to tell a program that.
>>55072930
What if someone were to write a function that generates a new state-vector from a current state combined with an input? Would that tickle your fancy?
FSMs are one of the nicest, easy to reason about ways to implement a lot of stuff imho
Bumpan because I need to understand this.
>>55072898
I don't really see the point of making your own FSM for string inputs when you already have implemented regexes in the language.
>>55073093
Me too. Regex is the perfect solution for searching a substring within a string.
>>55073093
I don't either. It's mandatory to take the test in 2 weeks though.
Even so, I didn't know I have regexes already implemented on Python.
>>55072898
Super easy..
I don't know python, but here's a Ruby solution.
Python way should be pretty similar..
(For the "switch"-statement you would probably use if-else-statements in python..)def number_in_FSM? (a)
# the state
state = "e0"
# ignore empty strings
return "fuck you!" if a.empty?
# get the elements as array
a = a.split
# check each element
a.each do |i|
# which state are we in ?
case state
when "e0"
if a[i] == 1
state = "e1"
elsif a[i] == 2
state = "e2"
else
return "not in the FSM, sorry.."
end
when "e1"
# some logic here
when "e2"
# some logic here
end
end
end
The principle is not difficult is it?
Of course you could also write a "state" class with the decision logic inside. This would be more robust, but a little bit verbose if the FSM is small. It depends on what you want with it..
By the way:
Google "state machine python", there are a lot of solutions out there..
>>55073231
OK, I found this solution in the internet, it's a FSM for a traffic lights.
>http://stackoverflow.com/questions/2101961/python-state-machine-design#answer-2103398
It's pretty neat!
Damn, I have to learn me some Python someday..# trafficLight.pystate
# define state machine
statemachine TrafficLight:
Red -> Green
Green -> Yellow
Yellow -> Red
# define some class level constants
Red.carsCanGo = False
Yellow.carsCanGo = True
Green.carsCanGo = True
Red.delay = wait(20)
Yellow.delay = wait(3)
Green.delay = wait(15)
And here's how to use it:import statemachine
import trafficLight
tl = trafficLight.Red()
for i in range(6):
print tl, "GO" if tl.carsCanGo else "STOP"
tl.delay()
tl = tl.next_state()
>>55073231
In python:def numFSM(a):
state='e0'
if a == '':
print('nigger')
else :
a = a.split()
for i in a:
if state == 'e0':
if i == 1:
state = 'e1'
elif i == 2:
state = 'e2'
else:
print('not in the FSM you nigger')
elif state == 'e1':
pass
elif state == 'e2':
pass
>>55073492
Thanks, short and beautiful.
>>55073492
>>55073575
>short and beautiful.
That code is the exact opposite of beautiful.
>>55072930
Remind me again why we allow Haskell fags to shit all over this board with their uneducated opinions?
>>55073587
I don't think he was serious m8
>>55073587
>That code is the exact opposite of beautiful.
It's not that bad.
I look at it and can immediately understand it.
If you put some comments in it it would pass as a "quick and dirty" solution..
Of course it would be better to have some kind of Enumeration of the states, but this depends on the size and purpose..
>>55072898
What is wrong with that picture?
>>55073492def numFSM(a):
state='e2'
if a == '':
print('[x] Error')
else :
a = a.split()
case0 = {i: 'e'+str(i) for i in range(0, len(a))}
#case1 = {#...}
#case2 = {#...}
while a :
for x in range(0, len(a)):
if state == 'e0':
state = case0[x]
print(state)
elif state == 'e1':
#state = case1[x]
print('case1')
elif state == 'e2':
#state = case2[x]
print('case2')
>>55072898
You might want to split it up into checking for transitions and actually acting according to the transitions:// some pseudo code
loop:
// check transitions
transition = notrans
if x: transition = xtrans
else if y: transition = ytrans
// change state
if transition = xtrans: doChangeStateX()
else if transition = ytrans: doChangeStateY()
else: doChangeStateDefault()
>>55072930
You are retarded.
