This is a summary of FSM implementations in Python right now.
For general information about finite state machines, see:
[wiki:WikiPedia/Finite_state_machine Wikipedia:Finite_state_machine] --
excellent! [wiki:Wiki/FiniteStateMachine FiniteStateMachine]
[http://fsme.sourceforge.net/ Finite State Machine Editor]
This is a tool where you can draw FSM diagrams, and then compile to a Python module (or C++ code.) It also makes an XML description of the FSM.
Requires QT for the editor. (Not the compiler, though, which probably reads XML.)
* [http://fsme.sourceforge.net/doc/tutorial.html tutorial] * [http://fsme.sourceforge.net/phpwiki/ project wiki]
[http://osteele.com/software/python/fsa/ FSA - Finite State Automation in Python]
This seems to be all about making FSMs, but I don't see a whole lot on how to use them!
[http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/146262 Noah Spurrier's FSM]
This is one found on ActiveState; It's purely Python code. You init an FSM, register transitions, and then throw inputs at it. States and inputs must be hashable.
You can also [http://www.noah.org/python/FSM/ find it on his website.]
[http://www.research.att.com/projects/mohri/fsm/doc4/fsmpy.html fsmpy module]
This seems to be a Python wrapper around [http://www.research.att.com/projects/mohri/fsm/ AT&T's FSM library.] It's all oriented around "weighted" finite state machines, so I'm not so sure how suitable it is if you just want to use unweighted FSM.
[http://wiki.python.org/moin/PythonDecoratorLibrary/ Decorator based FSM]
A decorator based FSM can be found in the Decorator Library on this site. The module simplifies implementaion of FSM's based on UML 2.0 state diagrams. The FSM is implemented as a class, with methods of the class associated with transitions or with states. The design is not the best for constructing FSMs to parse text being somewhat slower than alternatives.
SkipMontanaro's FSM
[http://www.python.org/search/hypermail/python-recent/0667.html From an e-mail.]
Features transition actions.
I've re-interpreted the code, adding formatting lost in e-mail, and PythonStyle-itizing it a bit.
1 """Finite state machine, featuring transition actions."""
2
3 FSMError = 'Invalid input to finite state machine'
4
5 class FSM:
6
7 """Finite state machine, featuring transition actions.
8
9 The class stores a dictionary of (state, input) keys,
10 and (state, action) values.
11
12 When a (state, input) search is performed:
13 * an exact match is checked first,
14 * (state, None) is checked next.
15
16 The action is of the following form:
17 * function(current_state, input)
18 """
19
20 def __init__(self):
21 self.states = {}
22 self.state = None
23 self.dbg = None
24
25 def add(self, state, input, newstate, action):
26 """Add a transition to the FSM."""
27 self.states[(state, input)] = (newstate, action)
28
29 def execute(self, input):
30 """Perform a transition and execute action."""
31 si = (self.state, input)
32 sn = (self.state, None)
33 # exact state match?
34 if self.states.has_key(si):
35 newstate, action = self.states[si]
36 # no, how about a None (catch-all) match?
37 elif self.states.has_key(sn):
38 newstate, action = self.states[sn]
39 if self.dbg != None:
40 self.dbg.write('State: %s / Input: %s /'
41 'Next State: %s / Action: %s\n' %
42 (self.state, input, newstate, action))
43 apply(action, (self.state, input))
44 self.state = newstate
45
46 def start(self, state):
47 """Define the start state.
48
49 Actually, this just resets the current state.
50 """
51 self.state = state
52
53 def debug(self, out):
54 """Assign a writable file to log transitions."""
55 self.dbg = out