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Re: class object's attribute is also the instance's attribute?

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On Thursday, August 30, 2012 4:30:59 PM UTC+2, Dave Angel wrote:
> On 08/30/2012 10:11 AM, Marco Nawijn wrote:
> 
> > On Thursday, August 30, 2012 3:25:52 PM UTC+2, Hans Mulder wrote:
> 
> >> <snip>
> 
> >>
> 
> > Learned my lesson today. Don't assume you know something. Test it first ;). I have done quite some programming in Python, but did not know that class attributes are still local to the instances. 
> 
> 
> 
> They're not.  They're just visible to the instances, except where the
> 
> instance has an instance attribute of the same name.  Don't be confused
> 
> by dir(), which shows both instance and class attributes.
> 
> 
> 
> Please show me an example where you think you observe each instance
> 
> getting a copy of the class attribute.  There's probably some other
> 
> explanation.

I don't have an example. It was just what I thought would happen. Consider the following. In a class declaration like this:

class A(object):
    attr_1 = 10

    def __init__(self):
       self.attr_2 = 20

If I instantiated it twice:

obj_1 = A()
obj_2 = A()

For both obj_1 and obj_2 attr_1 equals 10. What I thought would happen after the following statement:

obj_1.attr_1 = 12

is that obj_2.attr_1 also equals 12. This is what surprised me a little, that's all. 

Marco

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class object's attribute is also the instance's attribute? 陈伟 <chenwei.address@gmail.com> - 2012-08-30 03:55 -0700
  Re: class object's attribute is also the instance's attribute? Dave Angel <d@davea.name> - 2012-08-30 07:53 -0400
    Re: class object's attribute is also the instance's attribute? 陈伟 <chenwei.address@gmail.com> - 2012-08-30 05:57 -0700
    Re: class object's attribute is also the instance's attribute? 陈伟 <chenwei.address@gmail.com> - 2012-08-30 05:57 -0700
  Re: class object's attribute is also the instance's attribute? Ulrich Eckhardt <ulrich.eckhardt@dominolaser.com> - 2012-08-30 13:22 +0200
  Re: class object's attribute is also the instance's attribute? Marco Nawijn <nawijn@gmail.com> - 2012-08-30 05:34 -0700
    Re: class object's attribute is also the instance's attribute? Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2012-08-30 13:52 +0100
    Re: class object's attribute is also the instance's attribute? Hans Mulder <hansmu@xs4all.nl> - 2012-08-30 15:25 +0200
      Re: class object's attribute is also the instance's attribute? Marco Nawijn <nawijn@gmail.com> - 2012-08-30 07:11 -0700
        Re: class object's attribute is also the instance's attribute? Dave Angel <d@davea.name> - 2012-08-30 10:30 -0400
          Re: class object's attribute is also the instance's attribute? Marco Nawijn <nawijn@gmail.com> - 2012-08-30 07:48 -0700
            Re: class object's attribute is also the instance's attribute? Dave Angel <d@davea.name> - 2012-08-30 11:18 -0400
          Re: class object's attribute is also the instance's attribute? Marco Nawijn <nawijn@gmail.com> - 2012-08-30 07:48 -0700
            Re: class object's attribute is also the instance's attribute? Hans Mulder <hansmu@xs4all.nl> - 2012-08-30 17:20 +0200
              Re: class object's attribute is also the instance's attribute? Ben Finney <ben+python@benfinney.id.au> - 2012-08-31 09:58 +1000

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