Keyword arguments - strange behaviour?

[brian.bird at securetrading.com]

> Channelling the effbot, I think he was asking what namespace context
you
> expected the expression "arg=otherfunction(x)" to be evaluated in
when
> it's used at the time of a function call to dynamically create a new
> default value for arg.

Thanks, I realise now that's what was meant. I think I was just
assuming otherfunction() would be globally available - but that's not
something I want to go into since I can see now there will be problems
trying to define what python should do if it evaluated defaults at the
function call :)

I think I can now explain to someone why there are good reasons that
the default params are evaluated at the definition. However, I still
can't give a nice looking solution on how to re-write a function to
have empty mutable values as default arguments: eg.

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

How could I re-write this (especially if there are perhaps 20 optional
parameters,any number of which may have mutable defaults) without
writing 20 "if opt1 is None: opt1=[]" statements?

Brian