jld*_*ont 45 python state-machine fsm
与此Stack Overflow问题(C状态机设计)相关,Stack Overflow人员可以与我(以及社区)共享您的Python状态机设计技术吗？
目前,我正在寻找基于以下内容的引擎:
class TrackInfoHandler(object):
def __init__(self):
self._state="begin"
self._acc=""
## ================================== Event callbacks
def startElement(self, name, attrs):
self._dispatch(("startElement", name, attrs))
def characters(self, ch):
self._acc+=ch
def endElement(self, name):
self._dispatch(("endElement", self._acc))
self._acc=""
## ===================================
def _missingState(self, _event):
raise HandlerException("missing state(%s)" % self._state)
def _dispatch(self, event):
methodName="st_"+self._state
getattr(self, methodName, self._missingState)(event)
## =================================== State related callbacks
但我确信在利用Python的动态特性(例如动态调度)的同时,还有很多方法可以实现.
我正在接受"引擎"的设计技术,它接收基于机器"状态"的"事件"和"发送".
S.L*_*ott 39
我真的不明白这个问题.该国设计模式是相当清楚的.请参阅设计模式一书.
class SuperState( object ):
def someStatefulMethod( self ):
raise NotImplementedError()
def transitionRule( self, input ):
raise NotImplementedError()
class SomeState( SuperState ):
def someStatefulMethod( self ):
actually do something()
def transitionRule( self, input ):
return NextState()
这是非常常见的样板,用于Java,C++,Python(我也确定其他语言).
如果您的状态转换规则碰巧是微不足道的,那么有一些优化可以将转换规则本身推送到超类中.
请注意,我们需要有前向引用,因此我们按名称引用类,并用于eval将类名转换为实际的类.另一种方法是使转换规则实例变量而不是类变量,然后在定义所有类之后创建实例.
class State( object ):
def transitionRule( self, input ):
return eval(self.map[input])()
class S1( State ):
map = { "input": "S2", "other": "S3" }
pass # Overrides to state-specific methods
class S2( State ):
map = { "foo": "S1", "bar": "S2" }
class S3( State ):
map = { "quux": "S1" }
在某些情况下,您的事件并不像测试对象的相等性那么简单,因此更通用的转换规则是使用正确的函数 - 对象对列表.
class State( object ):
def transitionRule( self, input ):
next_states = [ s for f,s in self.map if f(input) ]
assert len(next_states) >= 1, "faulty transition rule"
return eval(next_states[0])()
class S1( State ):
map = [ (lambda x: x == "input", "S2"), (lambda x: x == "other", "S3" ) ]
class S2( State ):
map = [ (lambda x: "bar" <= x <= "foo", "S3"), (lambda x: True, "S1") ]
由于规则是按顺序评估的,因此允许使用"默认"规则.
Pau*_*McG 12
在2009年4月的Python杂志中,我写了一篇关于使用pyparsing和imputil在Python中嵌入State DSL的文章.此代码允许您编写模块trafficLight.pystate:
# 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)
并且DSL编译器将创建所有必需的TrafficLight,红色,黄色和绿色类,以及适当的状态转换方法.代码可以使用以下内容调用这些类:
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()
(不幸的是,imputil已经在Python 3中被删除了.)
我也对state_machines的当前选项不满意所以我编写了state_machine库.
您可以安装它pip install state_machine并像这样使用它:
@acts_as_state_machine
class Person():
name = 'Billy'
sleeping = State(initial=True)
running = State()
cleaning = State()
run = Event(from_states=sleeping, to_state=running)
cleanup = Event(from_states=running, to_state=cleaning)
sleep = Event(from_states=(running, cleaning), to_state=sleeping)
@before('sleep')
def do_one_thing(self):
print "{} is sleepy".format(self.name)
@before('sleep')
def do_another_thing(self):
print "{} is REALLY sleepy".format(self.name)
@after('sleep')
def snore(self):
print "Zzzzzzzzzzzz"
@after('sleep')
def big_snore(self):
print "Zzzzzzzzzzzzzzzzzzzzzz"
person = Person()
print person.current_state == person.sleeping # True
print person.is_sleeping # True
print person.is_running # False
person.run()
print person.is_running # True
person.sleep()
# Billy is sleepy
# Billy is REALLY sleepy
# Zzzzzzzzzzzz
# Zzzzzzzzzzzzzzzzzzzzzz
print person.is_sleeping # True