If a function calls itself, it is called a recursive function. In order to prevent it from falling in infinite loop, recursive call is place in a conditional statement.
Following program accepts a number as input from user and sends it as argument to rsum() function. It recursively calls itself by decrementing the argument each time till it reaches 1.
def rsum(n):
if n <= 1:
return n
else:
return n + rsum(n-1)
num = int(input("Enter a number: "))
ttl=rsum(num)
print("The sum is",ttl)Sample run of above program prints sum o natural numbers upto input number
Enter a number: 10 The sum is 55