Sum of integer from 1 to N using Recursion.

def func(num):
if num == 0:
return 0
return num + func(num - 1)

num = int(input())
res = func(num)
print(res)

Explanation:
num = 4

4 == 0 # false
4 @tsuri_girl_official+ func(3)

3 == 0 # false
4 + 3 + func(2)

2 == 0 # false
4 + 3 + 2 + func(1)

1 == 0 # false
4 + 3 + 2 + 1 + func(0)

0 == 0 # True
4 + 3 + 2 + 1 + 0
4 + 3 + 2 + 1
4 + 3 + 3
4 + 6
10

Output:
10