Order of object cleanup at interpreter exit?

[Rob W. W. Hooft]

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?
       
Rob Hooft
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