This is a summary of FSM implementations in Python right now.
For general information about finite state machines, see:
Wikipedia:Finite_state_machine --
excellent!
Contents
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.)
* tutorial * project wiki
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!
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 find it on his website.
This seems to be a Python wrapper around 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.
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
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