What is recursion in Python with Examples?

Recursion is the process of defining something in terms of itself. A recursive function is a function defined in terms of itself via self-referential expressions. This means that the function will go on to call itself and repeat its actions whereas some condition is met to return a result.

In other words we can say that it is a programming technique in which a function calls itself from its own body definition. It is similar to loop because it repeats the same code a number of times.

Advantages of Recursion

• Recursive functions make the code look clean and stylish.

• A complex task can be broken down into simpler sub-problems using recursion.

• Sequence generation is easier with recursion than using some nested iteration.

Disadvantages of Recursion

• Occasionally the logic behind recursion is hard to follow through.

• Recursive calls are costly because they are used a lot of memory and time.

• Recursive functions are not easy to debug.

Example:

Write a program to input a number and calculate its factorial.

def fact(x):

if x == 1:

return 1

else:

return (x * fact(x-1))

num=int(input("Enter the Number: "))

print("The factorial of", num, "is", fact(num))

Output:

Enter the Number: 3

The factorial of 3 is 6

Example 2:

Write a program to input a number and print its table up to 10 terms.

Program:

def table(num):

for i in range(1, 11):

print(num, 'x', i, '=', num*i)

return

n = int(input("Enter number: "))

table(n)

Output:

Enter number: 5

5 x 1 = 5

5 x 2 = 10

5 x 3 = 15

5 x 4 = 20

5 x 5 = 25

5 x 6 = 30

5 x 7 = 35

5 x 8 = 40

5 x 9 = 45

5 x 10 = 50

Example 3:

Python program calculates the sum of the first N Natural numbers using recursive function calls.

def sum(n):

if n==1:

return 1

else:

return (n + sum(n-1))

num=int(input("Enter a number : "))

s=sum(num)

print("The sum of natural numbers is ", s)

Output:

Enter a number : 4

The sum of natural numbers is 10