explanation plzzzz!!!

Question

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

print(func(4))

Answer 1

res = 0

for i in range(4) # i= 1, 2, 3

i= 0
res += i # res ----- 0
i = 1
res += i #res ----- 1
i= 2
res += i #res ----- 3
i = 3
res += i #res ----- 6

Answer 2

https://code.sololearn.com/cZ4dLuyx6BVv/#py