Re: help in understanding the stackless code

[MRAB]

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?

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