Learn the Techniques: How to Reverse a Number in Python Efficiently

Reversing a number in Python is a common task in programming and algorithm challenges. It involves rearranging the digits of a number so that the last digit becomes the first and the first becomes the last. Python provides multiple ways to achieve this efficiently, from arithmetic operations to loops and built-in functions. Knowing these techniques helps you solve coding problems faster and write cleaner code. 

In this guide, you'll read more about the concept of number reversal, step-by-step methods using arithmetic, string conversion, for and while loops, and functions. We’ll also explore advanced techniques like recursion and list comprehension, compare all methods for efficiency, and show practical applications.  

Shape your future with upGrad’s Data Science Course. Gain hands-on expertise in AI, Machine Learning, and Data Analytics to become a next-generation tech leader. Enroll today and accelerate your career growth.

Methods to Reverse a Number in Python

Reversing a number in Python can be done in several ways. Each method has its own advantages. You can choose based on your coding style, performance needs, or the problem you are solving. Below, we’ll explore the most common techniques with clear examples. 

1. Using Arithmetic Operations 

The arithmetic method uses modulus and floor division to extract and reverse digits. This approach works without converting the number into a string. 

Steps: 

• Take the last digit using % 10. 
• Add it to a new reversed number multiplied by 10. 
• Remove the last digit from the original number using // 10. 
• Repeat until the original number is 0. 

Example Code: 

num = 12345 
reversed_num = 0 
 
while num > 0: 
    digit = num % 10 
    reversed_num = reversed_num * 10 + digit 
    num = num // 10 
 
print("Reversed Number:", reversed_num) 

Output: 

Pros: No type conversion, efficient. 

Cons: Slightly more steps than string methods. 

Also Read: What are Assignment Operators in Python? 

2. Using String Conversion 

Python makes it simple by converting numbers into strings. You can reverse the string and convert it back to an integer. 

Example Code: 

num = 12345 
reversed_num = int(str(num)[::-1]) 
print("Reversed Number:", reversed_num) 
  

Output: 54321 

Pros: Very concise, easy for beginners. 

Cons: Involves type conversion.  

3. Using For Loop 

You can use a for loop to iterate over the digits of a number (after converting it to a string) and build the reversed number manually. 

Example Code: 

num = 12345 
reversed_num = 0 
 
for digit in str(num): 
    reversed_num = reversed_num * 10 + int(digit) 
 
print("Reversed Number:", reversed_num) 

Pros: Clear logic, beginner-friendly. 

Cons: Slightly longer code than slicing method. 

Also Read: Nested For Loop in Python: How It Works with Examples 

4. Using While Loop 

A while loop is similar to the arithmetic method but emphasizes iteration until a condition is met. 

Example Code: 

num = 12345 
reversed_num = 0 
 
while num != 0: 
    reversed_num = reversed_num * 10 + num % 10 
    num = num // 10 
 
print("Reversed Number:", reversed_num) 
  

This is ideal for dynamic input, where the number changes during runtime. 

Also Read: Python While Loop Statements: Explained With Examples 

5. Using Functions 

You can also create a reusable function for reversing numbers. 

Example Code: 

def reverse_number(num): 
    reversed_num = 0 
    while num > 0: 
        reversed_num = reversed_num * 10 + num % 10 
        num = num // 10 
    return reversed_num 
 
print(reverse_number(12345)) 

Pros: Makes your code modular and easy to reuse. 

Also Read: Most Important Python Functions [With Examples] | Types of Functions 

Comparison Table of Methods 

These methods cover all common ways to reverse a number in Python. Beginners can start with string conversion for simplicity, while advanced programmers might prefer arithmetic operations for performance. Using functions helps make your code cleaner and reusable.

Advanced Techniques to Reverse a Number in Python 

Once you are comfortable with the basic methods, Python also allows advanced techniques to reverse a number in Python efficiently. These approaches are useful when you want concise code, reusable functions, or are handling complex scenarios. 

1. Using Recursion 

Recursion lets a function call itself until a base condition is met. You can use recursion to reverse a number in Python by processing one digit at a time. 

Steps: 

• Extract the last digit using % 10. 
• Append it to the reversed number returned by the recursive call. 
• Stop recursion when the number becomes 0. 

Example Code: 

def reverse_number(num): 
    if num == 0: 
        return 0 
    else: 
        digits = len(str(num)) - 1 
        return (num % 10) * (10 ** digits) + reverse_number(num // 10) 
 
print(reverse_number(12345)) 
  

Output: 54321 

Pros: Elegant and demonstrates programming concepts. 

Cons: Slightly slower for very large numbers due to multiple function calls. 

Also Read: Top 50 Python Project Ideas with Source Code in 2025 

2. Using List Comprehension 

List comprehension can also be used to write a program to reverse a number in Python in a concise way. Convert the number to a string, iterate in reverse, and join the digits back. 

Example Code: 

num = 12345 
reversed_num = int(''.join([digit for digit in str(num)][::-1])) 
print(reversed_num) 
  

Output: 54321 

Pros: Short and clean code. 

Cons: Slightly less intuitive for beginners. 

3. Handling Large Numbers Efficiently 

For large numbers, performance varies depending on the method. Arithmetic operations are usually faster and use less memory than string conversion, recursion, or list comprehension. 

Performance Table: 

 4. Combining Methods for Flexibility 

You can combine methods depending on the scenario: 

• Use arithmetic operations for high-performance tasks. 
• Use string conversion or list comprehension for shorter code. 
• Use functions and recursion for reusable code and concept demonstration. 

Example: Recursive Function 

def reverse(num, rev=0): 
    if num == 0: 
        return rev 
    return reverse(num // 10, rev * 10 + num % 10) 
 
print(reverse(12345)) 

Output: 54321 

These advanced techniques allow you to reverse a number in Python efficiently while keeping your code readable and reusable. Beginners can start with recursion or list comprehension, while arithmetic operations are ideal for performance-critical tasks. 

Comparing All Methods 

After exploring the various ways to reverse a number in Python, it is helpful to compare them side by side. This allows you to choose the best method based on ease, performance, and readability. Each approach has its strengths and trade-offs. 

Key Comparison Points 

When deciding how to write a program to reverse a number in Python, consider: 

• Ease of Use: How simple is it for beginners? 
• Performance: How fast does it execute, especially for large numbers? 
• Memory Usage: Does it use extra space for conversions or recursion? 
• Readability: How easy is it to understand and maintain? 

Also Read: Why Learn Python – Top 10 Reasons to Learn Python in 2024 

Comparison Table 

Choosing the Right Method 

• Beginners: Start with string conversion or for loops. They are easy to understand and quick to implement. 
• Intermediate coders: Use while loops or function-based arithmetic methods for better control and performance. 
• Advanced programmers: Try recursion or list comprehension for concise code or concept practice. 

Tip: For coding interviews or competitive programming, arithmetic operations are preferred due to speed and low memory usage. 

This comparison ensures that beginners and advanced users can pick the right approach for their needs. 

Also Read: Python Challenges for Beginners 

Understanding the Concept of Number Reversal 

Before you start coding, it is important to understand what it means to reverse a number in Python. Number reversal is simply rearranging the digits of a number so that the last digit becomes the first, the second last becomes the second, and so on. For example, 12345 becomes 54321. 

Reversing numbers is a fundamental concept in programming. It helps you practice logic, loops, and arithmetic operations. You will encounter it often in coding challenges, algorithm problems, and Python exercises. 

Key Points to Remember 

When learning how to reverse a number in Python, keep these points in mind: 

• A number like 12345 reversed becomes 54321. 
• Leading zeros in the reversed number are usually removed (e.g., 120 → 21). 
• Negative numbers retain their sign (e.g., -123 → -321). 
• Python allows multiple ways to achieve this: arithmetic, string conversion, loops, recursion, and more. 

Also Read: Step-by-Step Guide to Learning Python for Data Science  

Original vs Reversed Number Table 

This table helps beginners see how numbers change when reversed. 

String vs Number Reversal 

It’s important to know the difference between reversing a number as an integer and reversing it as a string: 

• Integer reversal uses arithmetic operations to manipulate digits directly. 
• String reversal converts the number into a string, reverses the characters, then converts it back to an integer. 

Both approaches achieve the same result, but the methods are different in performance and readability. 

Common Challenges 

• Negative numbers: Ensure the minus sign stays at the beginning. 
• Leading zeros: Numbers like 1000 should reverse to 1, not 0001. 
• Input validation: Ensure the value is a number before attempting to reverse it. 

Also Read: Top 70 Python Interview Questions & Answers: Ultimate Guide 2025 

Summary: 

• Reverse digits without changing their values 
• Handle negatives correctly 
• Remove unnecessary leading zeros 
• Choose the method based on readability and efficiency 

Understanding these concepts lays a solid foundation. Once you grasp them, you can easily write a program to reverse a number in Python using any method. It also makes learning advanced techniques like loops, recursion, and functions more intuitive. 

Become an Expert at Python with upGrad! 

Reversing a number in Python requires choosing the right algorithm, as methods like recursion, loops, and slicing impact performance and efficiency. Experiment with different approaches like loops, recursion, and string manipulation to understand their trade-offs in efficiency.  

Struggling with choosing the proper method for complex problems? Consider upGrad’s additional courses to tackle challenges and gain expertise in algorithms and Python programming.  

• Generative AI Mastery Certificate for Software Development 
• Advanced SQL: Functions and Formulas 
• Introduction to Database Design with MySQL 

Curious which courses can help you strengthen your knowledge in Python? Contact upGrad for personalized counseling and valuable insights. For more details, you can also visit your nearest upGrad offline center.

Test Your Knowledge on Reversing Numbers in Python!

Assess your understanding of different methods to reverse a number in Python, including key concepts and practical use cases by answering the following multiple-choice questions. Challenge yourself and see how well you know Python's number reversal techniques! 

Test your knowledge now!

Q1. What is the simplest way to reverse a number in Python?
A) Using a for loop
B) Using string slicing
C) Using recursion
D) Using the reversed() method

Q2. Which Python method can you use to reverse a string?
A) reverse()
B) pop()
C) join()
D) split()

Q3. How does recursion help in reversing a number?
A) By repeatedly extracting the last digit and appending it
B) By reversing the number in-place
C) By using a loop to iterate through digits
D) By converting the number to a string

Q4. What happens if you reverse a number using the reverse() method in Python?
A) It returns a reversed list
B) It modifies the original number
C) It reverses the digits in-place
D) It raises an error

Q5. Which of the following is the correct syntax to reverse a number using string slicing?
A) str(num)[::-1]
B) num.reverse()
C) reverse(num)
D) num[::-1]

Q6. In which scenario would recursion be a better method for reversing a number in Python compared to other methods?
A) When working with very large numbers
B) When handling very simple number reversal tasks
C) When you want to test recursion techniques
D) When working with strings only

Q7. How do you reverse a number using the reversed() function?
A) reversed(str(num))
B) reversed(num)
C) num[::-1]
D) reverse(num)

Q8. Can you reverse a number using a list in Python?
A) No, lists do not support reversing
B) Yes, by converting the number to a list and using reverse()
C) Yes, by using a dictionary
D) No, you need a different data structure

Q9. What is the advantage of using a while loop to reverse a number in Python?
A) It’s faster than other methods
B) It avoids converting the number to a string
C) It’s simpler than using recursion
D) It automatically detects the length of the number

Q10. How can you reverse a number using the pop() method in Python?
A) By adding the digits to the list and popping them one by one
B) By using pop() in a while loop
C) By converting the number to a string and popping each character
D) pop() cannot be used for number reversal

Also read: Top 36+ Python Projects for Beginners and Students to Explore in 2025

Unlock the power of data with our popular Data Science courses, designed to make you proficient in analytics, machine learning, and big data!

Explore our Popular Data Science Courses

Elevate your career by learning essential Data Science skills such as statistical modeling, big data processing, predictive analytics, and SQL!

Top Data Science Skills to Learn

Stay informed and inspired with our popular Data Science articles, offering expert insights, trends, and practical tips for aspiring data professionals!

Read our popular Data Science Articles

Reference: 
https://content.techgig.com/technology/python-dominates-2025-programming-landscape-with-unprecedented-popularity/articleshow/121134781.cms