[Tutor] [cross product instead of nested loops]

[Daniel Yoo]

On Sun, 6 May 2001, Julieta Rangel wrote:

> I've been playing with the cross product definition you gave me. It makes a 
> lot of sense, and I'm sure it will make it a lot easier for me to prove 
> associativity; however, I'm doing something wrong because when I run it, I 
> don't get the result I thought I would.  Would you take a look and tell me 
> what I'm doing wrong?
> 
> 
> def cross(set1,set2):
>     resulting_set = []
>     for s1 in set1:
>         for s2 in set2:
>             resulting_set.append( (s1, s2) )
>             return resulting_set                 ## <-- bug!

There's a bug here: we want to return the resulting_set only after we
finish going through both for loops.  That is:

###
def cross(set1,set2):
    resulting_set = []
    for s1 in set1:
        for s2 in set2:
            resulting_set.append( (s1, s2) )
    return resulting_set
###

The difference is in indentation, but the idea is that the request about
returning a result should be outside of the looping.  After fixing this,
the program should work ok.