[ python-Bugs-1545463 ] New-style classes fail to cleanup attributes

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Bugs item #1545463, was opened at 2006-08-23 18:24
Message generated for change (Comment added) made by gbrandl
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Category: Python Interpreter Core
Group: Python 2.4
Status: Open
Resolution: None
Priority: 5
Submitted By: Alexander Belopolsky (belopolsky)
Assigned to: Nobody/Anonymous (nobody)
Summary: New-style classes fail to cleanup attributes

Initial Comment:
> cat x.py
class X(object):
    def __init__(self, x):
        self.x = x
        print 'creating X(%r)' % x

    def __del__(self):
        print 'deleting X(%r)' % self.x

class A(object):
    x = X('new')

class B:
    x = X('old')
> python x.py
creating X('new')
creating X('old')
deleting X('old')

Python 2.4.2 (#2, Jan 13 2006, 12:00:38)
Python 2.6a0 (trunk:51513M, Aug 23 2006, 14:17:11)

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>Comment By: Georg Brandl (gbrandl)
Date: 2006-08-23 23:18

Message:
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There's also this sentence in the __del__ docs:
"""
It is not guaranteed that __del__() methods are called for
objects that still exist when the interpreter exits.
"""

----------------------------------------------------------------------

Comment By: Alexander Belopolsky (belopolsky)
Date: 2006-08-23 22:54

Message:
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Yes, I've found that (using gc.get_referrers!), but this
does not explain why A is not cleaned up when the program exits.

Note that if I put class A definition inside a function, it
does get cleaned up.  Must be some funny interation between
module and new-style class objects.

----------------------------------------------------------------------

Comment By: Georg Brandl (gbrandl)
Date: 2006-08-23 22:45

Message:
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Note that new-style classes are always part of a reference
cycle (you can find this out via gc.get_referrers).
Therefore, they will not be deleted instantly, but only
after gc collects them (you can trigger that via gc.collect).

----------------------------------------------------------------------

Comment By: Alexander Belopolsky (belopolsky)
Date: 2006-08-23 22:01

Message:
Logged In: YES 
user_id=835142

It looks like the class object is not deleted alltogether:



class X(object):
    def __init__(self, x):
        self.x = x
        print 'creating X(%r)' % x

    def __del__(self):
        print 'deleting X(%r)' % self.x
        
class A(object):
    x = X('new')

del A

Output:
creating X('new')
deleting X('new')



----------------------------------------------------------------------

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