Program to Reverse a String in Python

October 13, 2022

What are strings and how to reverse a string?

The string is an immutable sequence data type. It is a sequence of Unicode characters wrapped inside a single, double or triple quote. The task is to write a program to reverse the given string.
Example :

  • Input : Hello world
  • Output: dlrow olleH
Reversing a String in python language

Program to Reverse a String using Python

There are three approaches to reverse a string variable in python.

  1. Using string slicing.
  2. Using reversed() function.
  3. Using Brute force.
Reversing a String Python Program

Method 1: Reversing a String using String slicing

Python code.

Run 
#using slicing:
string = "Hello world"
print(string[::-1])
Output
Hello world
dlrow olleH

Explanation

The slicing function accepts three variables in the format

  • [start:stop:step]

The start holds the starting index of the string, the stop holds the last-1 element’s index, step holds the value of the number of steps while iteration.

In the code, string[::-1], when we pass -1 as the step and the empty start and end take 0 and len(string)-1 by default. This reverses the string with step 1 in the reverse direction.

Method 2: Reversing a String using reversed() function

Python code

Run
string = "Hello world"
print(''.join(list(reversed(string))))
Output
Hello world
dlrow olleH

Explanation.
The reversed() takes string values and returns the reversed string.

  • reversed(string)

In the above code, we take string using input() function. input() function returns a list, which is stored in the string variable. We pass the list string in reversed() function which returns a list of reversed string elements. The string list is then converted to a string variable using .join() function.

Method 3: Reversing a string using brute force approach

Python code

Run
#using brute force:
string = "Hello world"
output = ''
for i in range(len(string)-1,1,-1):
  output+=string[i]
output+=string[i-1]
output+=string[i-2]
print(output)
Output
Hello world
dlrow olleH

Explanation
In the above code, we use brute force approach, the algorithm is as follows:

  1. Take string as input using input() function.
  2. Initialise an empty string output.
  3. Run a loop from last to first with step size as 1.
  4. Append the element to the output string using ‘+’ operator.
  5. Print the output using print() function.

The range() function in the for loop, accepts three variables,

  • range(start,stop,step)

We are iterating the whole string from the end hence, reversing the whole string.

 
 

Toggle each character in a string

Find the ASCII value of a character

Length of the string without using strlen() function

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