Understanding how is a function evaluated using recursion

[rusi]

On Thursday, September 26, 2013 4:54:22 AM UTC+5:30, Arturo B wrote:
> So I know what recursion is, but I don't know how is 
> 
>                        flatten(i)
> 
> evaluated, what value does it returns?

When you are a noob, who do you ask? The gurus.
When you are a guru who do you ask? The computer!

And its really quite easy to ask the computer directly. Here's your code with a extra prints

def flatten(l):
    print ("Received: %s" % l)
    ret = []
    for i in l:
        if isinstance(i, list) or isinstance(i, tuple):
            ret.extend(flatten(i)) #How is flatten(i) evaluated?
        else:
            ret.append(i)
    print ("Returning: %s" % ret)
    return ret 

Now run it with a couple of different inputs (not neglecting the trivial cases) and see if it does not self-explain.

If still confusing, come back and ask!