[Tutor] Testing print

[Alan Gauld]

On 01/10/16 23:08, boB Stepp wrote:
> On Sat, Oct 1, 2016 at 11:35 AM, Alan Gauld via Tutor <tutor at python.org> wrote:
> 
>> ... Personally I don't like functions that
>> sometimes return one and sometimes two results. I'd rather
>> you returned a None first argument in the first case
>> to make it consistent.
> 
> Why don't you like doing this?  What are the pluses and minuses as you
> see them?  


Because client code has to guess which return value is relevant

consider

def f(x):
   if x%2:  # is odd
      return x,x+1
   else: return x

Now I want to use f on a collection of integers:

nums = [1,2,3,4]

for n in nums:
    result = f(n)
    if result <= 3:   # broken for 1 and 3
       print("success")
    else: ....

But if I change it to

for n in nums:
    result = f(n)
    if result[0] <= 3: # now broken for 2 and 4
       print("success")
    else: ....

So I need to introduce code to determine whether I got
an int or a tuple back and then separate code for each
case. If I know that the result is always an int I can
use the first case if I know its always a tuple I can
use the second. But not knowing which is just plain
messy.



-- 
Alan G
Author of the Learn to Program web site
http://www.alan-g.me.uk/
http://www.amazon.com/author/alan_gauld
Follow my photo-blog on Flickr at:
http://www.flickr.com/photos/alangauldphotos