Question about my code

[snippsat]

What I don't understand in this solution is why the range is starting from 1 instead of 0?

It make no difference when summing it up,can look at range() to see what's going on.

>>> list(range(6))
[0, 1, 2, 3, 4, 5]
>>> list(range(0, 6))
[0, 1, 2, 3, 4, 5]
>>> list(range(1, 6))
[1, 2, 3, 4, 5] 

So Python(as most programming langues) start to count from 0.
When summing these up can use build sum() as you have written as a exercise,
then it will not be 21 because start a 0.

>>> sum(range(6))
15
>>> sum(range(0 ,6))
15
>>> sum(range(1, 6))
15
>>> 
>>> # So most add 1 to get 21,so starting a 0 or 1 make difference when use sum() or your code
>>> sum(range(7))
21
>>> sum(range(0 ,7))
21
>>> sum(range(1 ,7))
21