Python Program to Reverse a String

You can reverse a string in Python using slicing like this: reversed_string = original_string[::-1] which creates a new string with characters in reverse order.

Examples

Inputhello

Outputolleh

InputPython

OutputnohtyP

Input

Output

How to Think About It

To reverse a string, think about reading the characters from the end to the start. Instead of going from left to right, you go from right to left, collecting each character until you reach the beginning.

Algorithm

1

Get the input string from the user or a variable.

2

Start from the last character of the string.

3

Collect characters moving backward until the first character.

4

Combine these characters to form the reversed string.

5

Return or print the reversed string.

Code

python

original_string = input("Enter a string: ")
reversed_string = original_string[::-1]
print("Reversed string:", reversed_string)

Output

Enter a string: hello
Reversed string: olleh

Dry Run

Let's trace the string 'hello' through the code

1

Input string

original_string = 'hello'

2

Reverse using slicing

reversed_string = original_string[::-1] results in 'olleh'

3

Print result

Output: Reversed string: olleh

Index	Character
4	o
3	l
2	l
1	e
0	h

Why This Works

Step 1: Slicing with negative step

Using [::-1] tells Python to take the string from end to start stepping backwards by 1, effectively reversing it.

Step 2: Creating a new string

This slicing creates a new string with characters in reverse order without changing the original string.

Alternative Approaches

Using a loop

python

original_string = input("Enter a string: ")
reversed_string = ''
for char in original_string:
    reversed_string = char + reversed_string
print("Reversed string:", reversed_string)

This method builds the reversed string by adding each character to the front, but is less concise than slicing.

Using reversed() and join()

python

original_string = input("Enter a string: ")
reversed_string = ''.join(reversed(original_string))
print("Reversed string:", reversed_string)

This uses Python's built-in reversed() function and joins characters back into a string, which is clear and readable.

Complexity: O(n) time, O(n) space

Time Complexity

Reversing a string requires visiting each character once, so it takes linear time proportional to the string length.

Space Complexity

A new string is created to hold the reversed characters, so space used is also proportional to the string length.

Which Approach is Fastest?

Slicing [::-1] is the fastest and most concise method, while loops and reversed() are slightly slower but more explicit.

Approach	Time	Space	Best For
Slicing [::-1]	O(n)	O(n)	Quick and concise reversal
Loop building string	O(n)	O(n)	Understanding string immutability
reversed() + join()	O(n)	O(n)	Readable and Pythonic