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. -- http://mail.python.org/mailman/listinfo/python-list