recursive function call

[Peter Otten]

Nicolas Vigier wrote:

> Hello,
> 
> I have in my python script a function that look like this :
> 
> def my_function(arg1, arg2, opt1=0, opt2=1, opt3=42):
>         if type(arg1) is ListType:
>                 for a in arg1:
>                         my_function(a, arg2, opt1=opt1, opt2=opt2,
>                         opt3=opt3)
>                 return
>         if type(arg2) is ListType:
>                 for a in arg2:
>                         my_function(arg1, a, opt1=opt1, opt2=opt2,
>                         opt3=opt3)
>                 return
>          ... then here the real function code
> 
> I'm new to python, so I was wondering if there is a better way to do that.
> The reason for a recursive function here is to be able to give lists for
> the first 2 args (I could as well use only a simple 'for' without a
> recursive call). The problem I have here, is that as I'm working on this
> script, I often change the prototype of the function, and each time I
> have to think about changing the recursive call too. Is there a way that
> I can do a recursive call and say something like "keep all the same
> arguments except this one" ?

Here is a non-recursive approach: 

def tolist(arg):
    if isinstance(arg, list): 
        return arg
    return [arg]

def f(arg1, arg2, more_args):
    for arg1 in tolist(arg1):
        for arg2 in tolist(arg2):
            # real code

If it were my code I would omit the tolist() stuff and instead always pass
lists (or iterables) as the function's first two arguments.

Peter