[Tutor] Converting integers into digit sum (Python 3.3.0)

[Rafael Knuth]

Hej Steven,

thanks for the clarification.
I have two questions - one about map function and the other about return.

> So, in mathematics we might have a mapping between (let's say) counting
> numbers 1, 2, 3, 4, ... and the even numbers larger than fifty, 52, 54,
> 56, ... and so on. The mapping function is 50 + 2*x:
>
> x = 1 --> 50 + 2*1 = 52
> x = 2 --> 50 + 2*2 = 54
> x = 3 --> 50 + 2*3 = 56
> x = 4 --> 50 + 2*4 = 58
>
> and so on, where we might read the arrow --> as "maps to".
>
> So the fundamental idea is that we take a series of elements (in the
> above case, 1, 2, 3, ...) and a function, apply the function to each
> element in turn, and get back a series of transformed elements (52, 54,
> 56, ...) as the result.
>
> So in Python, we can do this with map. First we define a function to do
> the transformation, then pass it to map:
>
> def transform(n):
>     return 50 + 2*n
>
> result = map(transform, [1, 2, 3, 4])

#1 Question

In which cases should I use a map function instead of a for loop like
this for example:

def transform(n, m):
    for i in range (n, m):
        print (50 + 2*i)

transform(1,5)

>>>
52
54
56
58

> A thought comes to mind... an very important lesson is to learn the
> difference between return and print, and to prefer return.
>
> You have written a function that calculates the digit sum. But it is not
> *reusable* in other functions, since it cannot do anything but *print*
> the digit sum. What if you want to store the result in a variable, and
> print it later? Or print it twice? Or put it in a list? Or add one to
> it? You're screwed, the function is no use to you at all.

#2 Question

Strangely, I get entirely different results depending on whether I use
return or print within a function.
Example:

def transform(n, m):
    for i in range (n, m):
        print (50 + 2*i)

transform(1,5)

>>>
52
54
56
58

Versus:

def transform(n, m):
    for i in range(n, m):
        return (50 + 2*i)

print(transform(1,5))

>>>
52

Why do I get entirely different results in each case? &:
How do I prevent my loop from breaking after the first round when
using return instead of print?

All the best,

Raf