Re: Problems when destroy object which is referenced member objects ['LBBW': checked]

From: Holger Joukl (Holger.Joukl_at_LBBW.de)
Date: 02/19/04 

Date: Thu, 19 Feb 2004 15:36:07 +0100
To: python-list@python.org

I want to run this code that destroy testB and testB's member object
testA. But no object destroy. I know testA increase testB's reference
count, but why wouldn't python decrease testB's reference count? Had I
do wrong something? 

--
 http://mail.python.org/mailman/listinfo/python-list
 Hi,
the refcount _is_ actually decreased by python, as you can see if you add
some code:
Python 2.3.3 (#12, Feb 19 2004, 11:42:09)
[GCC 2.95.2 19991024 (release)] on sunos5
Type "help", "copyright", "credits" or "license" for more information.
>>> class TestA:
...     def __init__(self):
...         print "init TestA"
...     def __del__(self):
...         print "del TestA"
...     def SetEvent(self, event):
...         self.event = event
...
>>> class TestB:
...     def __init__(self):
...         print "init TestB"
...         self.testA = TestA()
...         self.testA.SetEvent(self.Test)
...     def __del__(self):
...         print "del TestB"
...     def Test(self):
...         pass
...     def __del__(self):
...         print "TestB.__del__"
...
>>> testB = TestB()
init TestB
init TestA
>>> print testB
<__main__.TestB instance at 0x1a75a8>
>>> import sys
>>> print sys.getrefcount(testB)
3
>>> # 1 more than expected because of testB given as function argument
... # This means after the return of getrefcount(), 2 references on
... # <__main__.TestB instance at 0x1a75a8> exist
... del testB
>>> # refcount is decreased but does not reach zero!
 As the reference count does not reach zero, the object is not destroyed
 (->destructor is not invoked, memory is not deallocated, but name
 testB is destroyed, so it is not accessible any more).
 You have a circular reference here, see python documention.
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