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import warnings
class FSM(object):
"""
Override Matcher and Handler and pass instances to add_handler to
create transitions between states. If a transition handles
something, it returns the next state.
If you want something to track global state, but it in your data
instance passed to process so that transitions, states can access
it.
"""
states = []
state = None
def __init__(self, states):
"""first state is the initial state"""
if len(states) > 0:
self.state = states[0]
self.states = states
def process(self, data):
#print self,"process",data
if self.state is None:
raise RuntimeError("There is no initial state.")
next_state = self.state.process(data)
if next_state:
#print "changing to",next_state.name,next_state
self.state = next_state
else:
warnings.warn("No next state", RuntimeWarning)
def add_state(self, state):
## first added state is initial state
if len(self.states) == 0:
self.state = state
self.states.append(state)
def dotty(self):
r = 'digraph fsm {\n\n'
for s in self.states:
r = r + s.dotty()
r = r + '\n}\n'
return r
class State(object):
def __init__(self, name):
self.name = name
self.transitions = []
def process(self, data):
#print self.name,"process",data
for t in self.transitions:
r = t.process(data)
if r is not None:
return r
return None
def add_transition(self, t):
self.transitions.append(t)
t.start_state = self
def add_transitions(self, transitions):
for t in transitions:
self.add_transition(t)
def __str__(self):
r = '<State %s [' % self.name
for t in self.transitions:
r = r + (' ->%s ' % t.next_state.name)
r = r + ']>'
return r
def dotty(self):
r = '%s;\n' % self.name
r = r + 'edge [fontsize=8]\n'
r = r + 'rankdir=TB;\nnodesep=2;\n'
for t in self.transitions:
r = r + '%s -> %s [label="%s\\n%s"]\n' % (self.name,
t.next_state.name,
t.matcher.__name__,
t.handler.__name__)
return r
class Transition(object):
def __init__(self, next_state, matcher, handler):
self.matcher = matcher
self.handler = handler
self.start_state = None
self.next_state = next_state
if self.next_state is None:
raise RuntimeError("next_state must be valid")
#print self,self.matcher,self.handler
def match(self, data):
"""
used by process; calls handler if matcher returns true for
data by default. may override instead of providing a matcher
methdo to ctor.
"""
#print self,"match",data,self.matcher
if self.matcher is not None:
return self.matcher(data)
return True
def handle(self, data):
"""
return next state. May override in a subclass to change
behavior or pass a handler method to ctor
"""
if self.handler:
state = self.handler(data)
#print "got",state
if state is None:
return self.next_state
return state
return self.next_state
def process(self, data):
"""return next state, or None if not handled."""
#print self,"process",data
if self.match(data):
return self.handle(data)
return None
def __str__(self):
if self.start_state:
return "<Transition %s->%s>" % (self.start_state.name,
self.next_state.name)
return "<Transition ->%s>" % (self.next_state.name,)
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