[Tutor] Default list arguments in __init__

[Moos Heintzen]

Hi,

This behavior was totally unexpected. I only caught it because it was 
the only thing I changed.

 >>> class foo:
...     def __init__(self, lst=[]):
...             self.items = lst
...
 >>> f1 = foo()
 >>> f1.items
[]
 >>> f1.items.append(1)
 >>> f2 = foo()
 >>> f2.items
[1]

Huh? lst is a reference to the *same list* every instance?

I guess I have to do it like this. It seems to work. (i.e. every foo 
instance with default lst now has a unique new list.)

def__init__(self, lst=None):
    self.items = lst or []


This is on python 2.4.4c1