initialization of lists in classes

[Fredrik Lundh]

Balint Aradi <ab007 at hszk.bme.hu> wrote:
>  I would like to ask something about initialization of lists in
> classes. Given the Python code
> 
> class test:
>     list = []
>     float = 3.2
> 
>     def __init__(self):
>         print 'list, float (#1):', self.list, self.float
>         self.list.append(1,2)
>         self.float = self.float + 2.0
>         print 'list, float (#2):', self.list, self.float

list is a shared class variable, not an instance variable.

until you know exactly how class variables behave,
make sure you initialize all your instance variables
in the constructor instead:

class test:
 
     def __init__(self):
         self.list = []
         self.float = 3.2
         print 'list, float (#1):', self.list, self.float
         self.list.append(1,2)
         self.float = self.float + 2.0
         print 'list, float (#2):', self.list, self.float

iirc, the FAQ has more info on class variables
and other issues related to shared mutable
variables.

</F>

coming soon:
http://www.pythonware.com/people/fredrik/librarybook.htm