How come this equals 6?

Question

Hi, I’m baffled by one of the module questions which was as followed:

def fun(x):
res = 0
for I in range(x):
res += I
return res
print(func(4))

Output: 6

One final thing, I played around with it in the code playground and I tried 5 and the answer was 10. Please could someone explain how this happens? Many thanks

Answer 1

#Your code will explain itself as follows
def func(x):
print('Input',x)
res = 0
print('output starts with',res)
for I in range(x):
print('add',I,'to',res,end=' ')
res += I
print('=',res)
return res
print(func(4))

Answer 2

It explains by the thing that "for" function takes all numbers from 0 to the range, in that case 4, but not including 4. The syntax from C++ will explain it better for(int i = 0; i < 4; i++). When i hits 4 it returns false, because 4 can't be smaller than 4, and the loop breaks without doing nothing more. If there would be i<=4, then 4 will be included.