How to Reverse a Number in Python

Reversing a number in Python can be done in various ways. Below are several methods to reverse a number in Python.

1. Converting the Number to a String

The simplest way to reverse a number is to convert it to a string, reverse the string, and then convert it back to an integer.

Example:

# Reversing a number by converting it to a string
num = 12345
reversed_num = int(str(num)[::-1])
print(reversed_num)

Output:

54321

In this example, the number 12345 is converted to the string "12345", which is then reversed to "54321" and converted back to the integer 54321.

2. Reversing a Number Using a While Loop

You can reverse a number mathematically by using a while loop. This method involves repeatedly extracting the last digit of the number and appending it to a new reversed number.

Example:

# Reversing a number using a while loop
num = 12345
reversed_num = 0

while num > 0:
    digit = num % 10
    reversed_num = reversed_num * 10 + digit
    num = num // 10

print(reversed_num)

Output:

54321

In this example, the number 12345 is reversed by repeatedly extracting the last digit and building the reversed number.

3. Using Recursion to Reverse a Number

Another method to reverse a number is by using recursion, which involves calling a function within itself.

Example:

# Reversing a number using recursion
def reverse_number(num, rev=0):
    if num == 0:
        return rev
    else:
        return reverse_number(num // 10, rev * 10 + num % 10)

num = 12345
reversed_num = reverse_number(num)
print(reversed_num)

Output:

54321

In this example, the reverse_number function reverses the number 12345 recursively by extracting digits and constructing the reversed number.

4. Using the map() and join() Functions

You can also reverse a number by converting it to a string, mapping each character back to an integer, and then joining them in reverse order.

Example:

# Reversing a number using map() and join()
num = 12345
reversed_num = int(''.join(map(str, reversed(str(num)))))
print(reversed_num)

Output:

54321

In this example, the number is first converted to a string, reversed, and then mapped back to a string before converting it to an integer.