Re: __del__ and reference count problem

[Terry Reedy]

"tiissa" <[EMAIL PROTECTED]> wrote in message 
news:[EMAIL PROTECTED]
> It's interesting to note that self.pop instead of A.pop works as 
> expected.
> But I don't know why A.pop doesn't.

Because the name 'A' is no longer associated with the class object. 
However, self has a reference to the class -- the .__class__ attribute. 
Since self does not itself have a .pop attribute, the attribute resolution 
code then looks at the class.

Terry J. Reedy



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Re: __del__ and reference count problem

[Terry Reedy]

<[EMAIL PROTECTED]> wrote in message 
news:[EMAIL PROTECTED]
> it looks like we have to use other way, hold the data we want to
> preseve in an object, because it is possible the class is removed
> before the instance cleaned,

What is removed first is the binding between name A and the class object. 
But the class object still exists (its refcount is > 0) and can be accessed 
via the instance which has a reference to that class object.

Terry J. Reedy



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Re: __del__ and reference count problem

[flupke]

[EMAIL PROTECTED] wrote:
look at this discussion:
http://www.dbforums.com/archive/index.php/t-1100372.html
it looks like we have to use other way, hold the data we want to
preseve in an object, because it is possible the class is removed
before the instance cleaned, and we can not expect __del__ 100% in
handling finalizing process.
Pujo
That forum helped. I changed this in my code and it worked
def __del__(self):
self.__class__.refcount -= 1
if (self.__class__.refcount == 0):
print "Last table standing"
else:
print "There is/are still %d table(s) left." % 
self.__class__.refcount

Output:
table <__main__.Table instance at 0x009D5B98>
refcount = 1
table <__main__.Table instance at 0x009D5BC0>
refcount = 2
Supplier returned from a 1: not implemented
Supplier returned from b 2: not implemented
There are 2 tables active.
There are 2 tables active.
There is/are still 1 table(s) left.
Last table standing
Seems to work allright !
Thanks ! :)
Benedict
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Re: __del__ and reference count problem

[[EMAIL PROTECTED]]

look at this discussion:
http://www.dbforums.com/archive/index.php/t-1100372.html

it looks like we have to use other way, hold the data we want to
preseve in an object, because it is possible the class is removed
before the instance cleaned, and we can not expect __del__ 100% in
handling finalizing process.

Pujo

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Re: __del__ and reference count problem

[tiissa]

[EMAIL PROTECTED] wrote:
Your problem can be simplified :
class A:
  pop = 11
  def __del__(self):
print A.pop
if __name__ == '__main__':
  objA = A()
I got the same error message, and I don't know why ? it looks like the
class variable can't be accessed from __del__?
It's interesting to note that self.pop instead of A.pop works as expected.
But I don't know why A.pop doesn't.
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Re: __del__ and reference count problem

[Fredrik Lundh]

[EMAIL PROTECTED] wrote:
Your problem can be simplified :
class A:
 pop = 11
 def __del__(self):
   print A.pop
if __name__ == '__main__':
 objA = A()
Exception exceptions.AttributeError: "'NoneType' object has no
attribute 'pop'" in > ignored
I got the same error message, and I don't know why ? it looks like the
class variable can't be accessed from __del__?
when Python shuts down, modules are sometimes cleaned out before objects
created from classes in those modules.  if you really need to access a global
object during finalization, you have to hold on to it yourself.
   def __del__(self, A=A):
   print A.pop
(the best solution is to avoid using finalizers, of course, but that's another 
story)

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Re: __del__ and reference count problem

[[EMAIL PROTECTED]]

Your problem can be simplified :

class A:
  pop = 11
  def __del__(self):
print A.pop

if __name__ == '__main__':
  objA = A()

Exception exceptions.AttributeError: "'NoneType' object has no
attribute 'pop'" in > ignored

I got the same error message, and I don't know why ? it looks like the
class variable can't be accessed from __del__?


Pujo

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__del__ and reference count problem

[flupke]

Hi,
i'm starting work and a simple database layer and wanted to use the 
__del__ to open and close a connection. However, i get an erro when 
executing this script:

class Table:
refcount = 0
def __init__(self, name):
self.name = name
print "table %s " % repr(self)
Table.refcount += 1
print "refcount = %s" % str(Table.refcount)
def __del__(self):
Table.refcount -= 1
if (Table.refcount == 0):
print "Last table standing"
else:
print "There is/are still %d table(s) left." % Table.refcount
def __getitem__(self,item):
return "not implemented"
def howMany(self):
if (Table.refcount == 1):
print "Only 1 table"
else:
print "There are %d tables active." % Table.refcount
if __name__ == '__main__':
suppliera = Table("suppliers")
supplierb = Table("suppliers")
print "Supplier returned from a %s: %s" % (1, suppliera[1])
print "Supplier returned from b %s: %s" % (2, supplierb[2])
suppliera.howMany()
supplierb.howMany()
This produces the following output and error:
table <__main__.Table instance at 0x008D5C10>
refcount = 1
table <__main__.Table instance at 0x008D5C38>
refcount = 2
Supplier returned from a 1: not implemented
Supplier returned from b 2: not implemented
There are 2 tables active.
There are 2 tables active.
Exception exceptions.AttributeError: "'NoneType' object has no attribute 
'refcount'" in > ignored
Exception exceptions.AttributeError: "'NoneType' object has no attribute 
'refcount'" in > ignored

What am i doing wrong?
Thanks
Benedict
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