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weird exceptions:(

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Join Date: Aug 2005

Posts: 148

Reputation: Micko is on a distinguished road

Solved Threads: 6

Micko

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Junior Poster

weird exceptions :(

Aug 30th, 2005

Hello, I'm trying to execute this simple code:

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class Person:
  population = 0
  def __init__(self, name):
    print 'Creating % s peron' % name
    self.name = name
    Person.population += 1
  def __del__(self):
    print 'Destroying %s person' % self.name
    Person.population -= 1
 
 
prvi = Person('Asimi')
drugi = Person('Mici')
class Person:
  population = 0
  def __init__(self, name):
    print 'Creating % s peron' % name
    self.name = name
    Person.population += 1
  def __del__(self):
    print 'Destroying %s person' % self.name
    Person.population -= 1
    
 
prvi = Person('Asimi')
drugi = Person('Mici')

I'm using Wing IDE trial and here's what is output in debug mode:

Creating Asimi peron
Creating Mici peron
Destroying Mici person
Exception exceptions.AttributeError: "'NoneType' object has no attribute 'population'" in <bound method Person.__del__ of <__main__.Person instance at 0x00B29558>> ignored
Destroying Asimi person
Exception exceptions.AttributeError: "'NoneType' object has no attribute 'population'" in <bound method Person.__del__ of <__main__.Person instance at 0x00B29530>> ignored

Problem is solved by putting self.population - = 1 in __del__ method, but the example is from book ByteOfPython and population is supposed to be class variable...

I really don't have a clue what is wrong here...

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Join Date: Jun 2005

Posts: 146

Reputation: G-Do is an unknown quantity at this point

Solved Threads: 28

G-Do

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Junior Poster

Re: weird exceptions:(

Sep 1st, 2005

It looks like you haven't included all the code you wrote to test this. Were there statements after 'drugi = Person('Mici')'? Statements like, perhaps:

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del drugi
del prvi

If so, please include them, because the other code worked fine for me.

Vi veri veniversum vivus vici

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Join Date: Oct 2004

Posts: 3,856

Reputation: vegaseat is just really nice

Solved Threads: 866

vegaseat

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DaniWeb's Hypocrite

Re: weird exceptions:(

Sep 1st, 2005

Look at variable k in the code snippet at:
http://www.daniweb.com/code/snippet354.html
This is a similar situation, it is declared outside of the class methods and needs self to bring it into the methods. The class name won't do. If your book uses this, then it is wrong (can happen). Maybe very early versions of Python allowed this.

Remember, special method __init__() is called first and acts as constructor. Special method __del__() acts as the mostly optional destructor.

May 'the Google' be with you!