# Python Coding challenge - Day 169 | What is the output of the following Python Code?

### Code:

def sum(num):
if num == 1:
return 1
return num + sum(num-1)
print(sum(4))

### Solution and Explanantion:

This is a recursive Python function named sum. It calculates the sum of integers from 1 to a given number (num). Let's break it down:

def sum(num)::

This line defines a function named sum that takes one argument, num.

if num == 1::

This is a base case for the recursion. It checks if the input num is equal to 1.

return 1:

If num is indeed 1, it returns 1. This is the base case of the recursion where the sum of integers from 1 to 1 is 1.

return num + sum(num-1):

If num is not equal to 1, it returns the sum of num and the result of calling sum recursively with num-1. This line adds the current value of num to the sum of all integers from 1 to num-1.

print(sum(4)):

This line calls the sum function with the argument 4, meaning it will calculate the sum of integers from 1 to 4.

Let's trace how this works with sum(4):

sum(4) calls sum(3)

sum(3) calls sum(2)

sum(2) calls sum(1)

sum(1) returns 1 (base case)

sum(2) returns 2 + 1 = 3

sum(3) returns 3 + 3 = 6

sum(4) returns 4 + 6 = 10

So, print(sum(4)) will output 10.