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Mon Sep 1 12:34:26 EDT 2003 · http://mail.python.org/pipermail/python-list/2003-September/184433.html

vincent delft wrote:
> Sorry if my question is stupid.
> I've missed something with classes. 
> Can you explain the following ?
> class test:
>   var1=1
>   var2=2
>   res=var1+var2
> 
> t=test()
> print t.res
> 
>>>3

Until here, t.var1 means test.var1 (class variable)

> t.var1=6

 From here, you created a new instance variable for object t, named 
var1. It hides test.var1.

> print t.res
> 
>>>3

What would you expect ?
1/ assigning to t.var1 does not modify test.var1
2/ modifiying test.var1 would not modify test.res anyway ! Guess why ?

Try this instead :
 >>> class test:
...     def __init__(self):
...         # create instance variables
...         self.var1 = 1
...         self.var2 = 2
...     def res(self):
...         return self.var1 + self.var2
...
 >>> t = test()
 >>> t.res()
3
 >>> t.var1 = 6
 >>> t.res()
8

Bruno

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HELP : class and variables