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Order of object cleanup at interpreter exit?

Michael Hudson mwh21 at cam.ac.uk
Mon Feb 14 04:44:53 EST 2000 
rob at hooft.net (Rob W. W. Hooft) writes:

> I am writing a package (98% python) that controls an analytical robot.
> The robot is controlled via a simple text protocol over a socket
> connection.
> 
> When the robot control object is garbage-collected, the __del__ method
> takes care of a proper termination of the socket connection by sending
> a last "EXIT" command:
> 
> def sendfixed(sock,data):
>     l=0
>     while l<len(data):
> 	l=l+sock.send(data[l:])
> 
> class Robot:
>     def __del__(self):
> 	if self.status>0:
> 	    sendfixed(self.sock1,'EXIT')
> 	    self.status=-1
> 
> 
> I have noticed that this does not work if the __del__ method is called
> when the interpreter is exiting (i.e., when I am using a Robot() object
> in the __main__ module at the global scope). I get:
> 
> Exception exceptions.TypeError: 'call of non-function (type None)' in 
>  <method Robot.__del__ of Robot instance at 81c8778> ignored
> 
> And indeed, it seems that the "sendfixed" function was already garbage
> collected: "print sendfixed" just before the call reports "None"....
> 
> I was not aware that it was "illegal" to call a function from a destructor.
> Is this a strange caveat? Bug? Feature? Any way to avoid it?

Try this:

    def __del__(self,sendfixed=sendfixed):
	if self.status>0:
	    sendfixed(self.sock1,'EXIT')
	    self.status=-1

That way, sendfixed shouldn't get collected before the instance
object.

Maybe a FAQ entry, except it's not very F Aed.

HTH,
Michael
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