Q: List and Dicts as default args

[Stefan Migowsky]

Hi,

I was just wondering how to handle lists and dictionaries in 
a simple way as default arguments to functions. Since following
strange behaviour occured :

>>> def f(Index,List = [], Dict = {}):
...     List.append(1)
...     List.append(2)
...     print List
...     Dict[Index] = Index
...     print Dict
>>> f(1)
[1, 2]
{1: 1}
>>> f(2)
[1, 2, 1, 2]
{2: 2, 1: 1}
>>> f(3)
[1, 2, 1, 2, 1, 2]
{3: 3, 2: 2, 1: 1}

This behaviour only occurs with dictionaries and list. All other
types are "well" behaved. I could try the following but that 
doesn't look so nice: 

def f(Index,List = None, Dict = None):
    if not List: List = []
    List.append(1)
    List.append(2)
    print List
    if not Dict: Dict = {}
    Dict[Index] = Index
    print Dict


Thanks for any advice.

	Stefan