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# -*- coding: utf-8 -*-
from __future__ import absolute_import
from __future__ import print_function
from __future__ import with_statement
import warnings
class FSM(object):
"""
Pass callables for matcher and handler to add_handler to create
transitions between states. A "matcher" is a predicate, and if a
transition handles something, it returns the next state.
If you want something to track global state, put it in your data
instance passed to process so that transitions and states can
access it.
Example:
idle = State("IDLE")
stuff = State("STUFF")
def is_capital(letter):
return letter in string.uppercase
def is_small(letter):
return letter in string.lowercase
def do_something_with_capitals(letter):
print("Got capital:", letter)
return stuff
idle.add_transition(
Transition(stuff, is_capital, self.do_something_with_capitals)
)
stuff.add_transition(
Transition(idle, is_lower, None)
)
"""
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):
if self.state is None:
raise RuntimeError("There is no initial state.")
next_state = self.state.process(data)
if 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):
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")
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.
"""
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)
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."""
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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