Could someone explain how the output is 6?

Question

def func(x):
res = 0
for i in range(x):
res += i
return res

print(func(4))

Answer 1

0+1+2+3

Answer 2

When range is used like this: range(x) it generates the interval of integers [0, x) {0 included, x excluded}. Therefore, calling func(4) adds the numbers in [0, 4) so
0+1+2+3=6.