Keyword arguments - strange behaviour?

[brian.bird at securetrading.com]

Thanks, this makes perfect sense. The phrase which sums it up neatly is
"Default parameter values are evaluated when the function definition is
executed"

However, is there a good reason why default parameters aren't evaluated
as the function is called? (apart from efficiency and backwards
compatibility)? Is this something that's likely to stay the same in
python3.0?

I'm really looking for a neat way to do the following:

def method(a,b,opt1=None,opt2=None,opt3="",opt4=None):
if opt1 is None: opt1=[]
if opt2 is None: opt2={}
if opt4 is None: opt4=[]

Python syntax is normally so neat but this just looks a mess if there
are lots of parameters.