Class Chaos

Helmut Jarausch jarausch at igpm.rwth-aachen.de
Mon Jun 28 12:06:50 CEST 2004


Maximilian Michel wrote:
> Hallo everyone, 
> 
> i hope someone can help me with this kind a interesting problem i have
> in python 2.3:
> 
> my code looks like this:
> 
> class Read:
>      list = []
>      __init__(self):
>               self.list.append = ***data from file***
>      print(self):
>               print self.list
> 
> instantiating it one time works ok, assuming data from file = AAA:
>        ...
>        a = Read()
>        AAA
> but when i continue, instantiating more object of the Read class this
> happens:
>        b = Read()
>        AAA
>        AAA
>        c = Read()
>        AAA
>        AAA
>        AAA
> it's like the new instance always continues or reimports the data from
> the former instance.

The assignment   list=[]  is made only once when the class definition
gets compiled. So your __init__ method uses one and the same list object
all the time.
When you create a new object of class 'Read' only the __init__ method gets
executed.
If you shift the 'list=[]' statement within the __init__ method it will
work as you probably like it to.

-- 
Helmut Jarausch

Lehrstuhl fuer Numerische Mathematik
RWTH - Aachen University
D 52056 Aachen, Germany



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