help in understanding the stackless code

[ravi]

yes It has instance of both Reporter and Switch.
moreover I could not get why instance "reporter" is passed to class Switch 
as a parameter ?

> >      reporter = Reporter()
> >      switch = Switch(0,reporter)
> >      switch(1)


thanks



On Thursday, June 18, 2015 at 5:45:08 PM UTC+5:30, MRAB wrote:
> On 2015-06-18 08:41, ravi wrote:
> > hi,
> > I am new to python and need to know why the calling of switch(1) invokes the function "listen" twice in the below program?
> >
> >
> >
> > import stackless
> >
> > class EventHandler:
> >      def __init__(self,*outputs):
> >          if outputs==None:
> >              self.outputs=[]
> >          else:
> >              self.outputs=list(outputs)
> >
> >          self.channel = stackless.channel()
> >          stackless.tasklet(self.listen)()
> >
> >      def listen(self):
> >          print "in listen()..."
> >          while 1:
> >              val = self.channel.receive()
> >              self.processMessage(val)
> >              for output in self.outputs:
> >                  self.notify(output)
> >
> >      def processMessage(self,val):
> >          pass
> >
> >      def notify(self,output):
> >          pass
> >
> >      def registerOutput(self,output):
> >          print "in registerOutput()..."
> >          self.outputs.append(output)
> >
> >      def __call__(self,val):
> >          print "in __call__ ..."
> >          self.channel.send(val)
> >
> > class Switch(EventHandler):
> >      def __init__(self,initialState=0,*outputs):
> >          EventHandler.__init__(self,*outputs)
> >          self.state = initialState
> >
> >      def processMessage(self,val):
> >          print "in processMessage() of Switch..."
> >          self.state = val
> >
> >      def notify(self,output):
> >          print "in notify() of switch..."
> >          output((self,self.state))
> >
> > class Reporter(EventHandler):
> >      def __init__(self,msg="%(sender)s send message %(value)s"):
> >          EventHandler.__init__(self)
> >          self.msg = msg
> >
> >      def processMessage(self,msg):
> >          print "in processMessage() of Reporter..."
> >          sender,value=msg
> >          print self.msg % {'sender':sender,'value':value}
> >
> >
> > if __name__ == "__main__":
> >      reporter = Reporter()
> >      switch = Switch(0,reporter)
> >      switch(1)
> >
> >
> >
> >
> > output:
> > =========
> >
> > in __call__ ...
> > in listen()...
> > in listen()...
> > in processMessage() of Switch...
> > in notify() of switch...
> > in __call__ ...
> > in processMessage() of Reporter...
> > <__main__.Switch instance at 0x8d822cc> send message 1
> >
> Is it because EventHandler has 2 subclasses, namely Switch and
> Reporter, and you have an instance of each?