Python Program to Reverse a Number

This article discloses how to write the Python Program to Reverse a Number using the While Loop, Functions, slicing, and Recursion.

Python Program to Reverse a Number Using While Loop

This Python program to reverse a number allows the user to enter any positive integer using a while loop. This program iterates each digit to inverse them.

Number = int(input("Please Enter any Number: "))
Reverse = 0
while(Number > 0):
    Reminder = Number %10
    Reverse = (Reverse *10) + Reminder
    Number = Number //10

print("\n Reverse of entered number is = %d" %Reverse)

Please Enter any Number: 1456

 Reverse of entered number is = 6541

This program allows the user to enter any positive integer. Then that number is assigned to a variable Number.

Next, Condition in the Python While loop makes sure that the given number is greater than 0.

From the above Python example program, User Entered integer value: Number = 1456 and Reverse = 0

First Iteration

Reminder= Number%10
Reminder= 1456%10 = 6

Reverse= Reverse*10 + Reminder
Reverse= 0 * 10 + 6  = 0 + 6 = 6

Number= Number//10
Number= 1456 //10 = 145

Second Iteration
From the While Loop first Iteration, the values of both the Number and Reverse changed as Number= 145 and Reverse= 6

Reminder= Number% 10
Reminder= 145 % 10 = 5

Reverse= Reverse*10 + Reminder = 6 * 10 + 5
Reverse = 60 + 5 = 65

Number= 145 //10 = 14

Third Iteration
From the Second Iteration of Python reverse the int Number program, Number= 14 and Reverse= 65

Reminder= 14%10 = 4

Reverse= 65 * 10 + 4 => 650 + 4 = 654

Number= 14//10 = 1

Fourth Iteration
From the third Iteration, Number = 1 and Reverse = 654

Reminder = 1 %10 = 1

Reverse= 654 * 10 + 1 => 6540 + 1 = 6541

Number= 1//10 = 0

Here, For the next iteration, Number= 0. So, the while loop condition fails. So, the final output is 6541.

Python Program to Reverse a Number using for loop

This program uses for loop range to iterate digits in a number and reverses them.

num = int(input("Enter any Number = "))

rv = 0

for i in range(len(str(num))):
    rv = rv * 10 + num % 10
    num = num // 10

print("The Result = ", rv)

Enter any Number = 12345
The Result =  54321

Python Program to Reverse a Number using Functions

This Python program allows the user to enter any positive integer and then we going to reverse an int number using the Functions.

def rev_Integer(num):
    rev = 0
    while(num > 0):
        rem = num %10
        rev = (rev *10) + rem
        num = num //10
    return rev

num = int(input("Please Enter any Num: "))
rev = rev_Integer(num)
print("\n Result = %d" %rev)

Please Enter any Num: 234589

 Reverse = 985432

Within this program, When it reaches to rev = rev_Integer (num) line in the program then, the compiler immediately jumps to the below function:

def rev_Integer(Number):

The last line ends with a return Reverse statement.

Python Program to Reverse a Number using slicing

In this example, str(num) will convert the given number to a string, and the [::-1] will slice the string and return characters in reverse. Next, the int() function will convert that reversed digits back to the integer.

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

rev = int(str(num)[::-1])

print("Result = ", rev)

Enter any Number: 23987
Result =  78932

Python Program to Reverse a Number using Recursion

This program allows the user to enter any positive integer. And then, we are going to reverse a number using Recursion.

rv = 0
def rv_Int(nm):
    global rv
    if(nm > 0):
        Reminder = nm %10
        rv = (rv *10) + Reminder
        rv_Int(nm //10)
    return rv

nm = int(input("Please Enter any Value : "))
rv = rv_Int(nm)
print("\n The Result of entered is = %d" %rv)

In this example, When the compiler reaches to rv = rv_Int(nm) line in the program, then the compiler immediately jumps to the below function:

def rv_Int(nm):

In this function, the below statement helps to call the function Recursively with the updated value. If you miss this statement, it terminates after completing the first line.

Rerv_Int(nm //10)

For example, Number = 459 produces the output as 9

Let’s see the If Statement,

if (nm > 0), check whether the number is greater than 0 or not. For Recursive functions, placing a condition before using the function recursively is essential. Otherwise, we end up in infinite execution (Same as an infinite Loop).

Using recursion Example 2

def rev_int(n):
    if n < 10:
        return n
    else:
        return int(str(n % 10) + str(rev_int(n // 10)))

num = int(input("Enter any Value = "))
rv = rev_int(num)
print("The Result = ", rv)

Enter any Value = 12345
The Result =  54321

Using list Comprehension

This example code uses the list comprehension and reversed function.

num = int(input("Enter any Number = "))

rv = int(''.join([str(i) for i in reversed(str(num))]))

print("The Result = ", rv)

Enter any Number = 98487
The Result =  78489