Python Recursion Example | Recursion In Python Programming

Python Recursion is the method of programming or coding the problem, in which the  function calls itself one or more times in its body. Usually, it is returning a return value of this function call. If the function definition satisfies the condition of recursion, we call this function a recursive function.

Working of Recursion in Python

def recurse():
    ...
    recurse()
    ...

recurse()

The recurse() function calls itself over and over again. The figure below shows how recursion works.

Example: Recursion

def greet():
    print('Hello')

    # recursive call
    greet()

# normal function call
greet()

Output

Hello Hello Hello Hello .. ..

The above program will call itself infinitely. Hence, we must include a stopping condition to stop the recursive call.

Stopping Condition for Recursion

If we do not include a stopping condition to stop the recursive call, the function will keep calling itself infinitely.

We generally use the if...else statement to stop the recursion.

def recurse():
    
    if condition: 
        # condition to break recursion
    
    else:
        # recursive call
        recurse()

In the above code, the if statement stops the recursive call and the else statement calls the function recursively.

Example: Recursion With Stop Condition

def print_number(number):
    
    # print number
    print(number)

    # stopping condition 
    if number == 0:
        print('Stop Printing') 
    else: 
        # recursive call 
        print_number(number - 1) 
        
print_number(2)        

Output

2
1
0
Stop Printing

In the above example, we have created a recursive function named print_number(). Here, the function calls itself until the number passed to it becomes 0.

Working of the code:

Example: Sum of Natural Numbers

def calculate_sum(num):

    # stopping condition
    if num == 1:
        return 1

    # recursive call
    return num + calculate_sum(num - 1)
    
result = calculate_sum(4)
print(result) 

Output

10

The calculate_sum(num) function calculates the sum of all integers from num to 1 using recursion.

If num equals 1, it simply returns 1 since that's the base case. Otherwise, it returns num plus the result of a recursive call to calculate_sum(num - 1).

Here, calculate_sum(4) computes the sum of 4, 3, 2, and 1, which is 10.

Working of the Sum of Natural Numbers

Advantages and Disadvantages of Recursion

The advantages and disadvantages of using recursion in Python are as follows:

Advantages

• Recursion makes our code shorter and cleaner.
• It is required in data structures and algorithms, such as Graph and Tree Traversal.

Disadvantages

• Recursion uses more processor time.
• Recursive functions are more difficult to debug compared to an equivalent iterative program.

Learn More:

In this tutorial, we will talk about recursion and how we can use it to divide and conquer!  We will also see which is faster - recursive functions or for loops?? we will compare between the two by recreating the Fibonacci Sequence and running a speed test!

⏰ TIME STAMPS ⏰
***************************
00:00 - Intro
00:15 - What is Recursion
01:03 - Python Recursive Function Code Example
02:43 - Fibonacci Sequence 
03:49 - Fibonacci Recursion Code Example
05:21 - Fibonacci Iteration Code Example
06:56 - Is Python Recursion Faster than Iteration?
08:25 - Divide and Conquer 
08:48 - Thanks for Watching!

#python #python recursion