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Reverse string in Python (6 different ways)

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  • Difficulty Level : Easy
  • Last Updated : 20 Jul, 2022

Python string library doesn’t support the in-built “reverse()” as done by other python containers like list, hence knowing other methods to reverse string can prove to be useful. This article discusses several ways to achieve it in Python

Example:

Input:  Geeksforgeeks
Output: skeegrofskeeG

Method 1: Reverse a string in Python using a loop

In this example, we call a function to reverse a string, which iterates to every element and intelligently joins each character in the beginning so as to obtain the reversed string. 

Time complexity: O(n) 
Auxiliary Space: O(1) 

Implementation:

Python3




def reverse(s):
    str = ""
    for i in s:
        str = i + str
    return str
 
s = "Geeksforgeeks"
 
print("The original string is : ", end="")
print(s)
 
print("The reversed string(using loops) is : ", end="")
print(reverse(s))

Output

The original string is : Geeksforgeeks
The reversed string(using loops) is : skeegrofskeeG

Method 2: Reverse a string in Python using recursion

The string is passed as an argument to a recursive function to reverse the string. In the function, the base condition is that if the length of the string is equal to 0, the string is returned. If not equal to 0, the reverse function is recursively called to slice the part of the string except the first character and concatenate the first character to the end of the sliced string. ‘

Time complexity: O(n) 
Auxiliary Space: O(n) 

Implementation:

Python3




def reverse(s):
    if len(s) == 0:
        return s
    else:
        return reverse(s[1:]) + s[0]
 
 
s = "Geeksforgeeks"
 
print("The original string is : ", end="")
print(s)
 
print("The reversed string(using recursion) is : ", end="")
print(reverse(s))

Output

The original string is : Geeksforgeeks
The reversed string(using recursion) is : skeegrofskeeG

Method 3: Reverse string in Python using stack

An empty stack is created. One by one character of the string is pushed to the stack. One by one all characters from the stack are popped and put back to a string. 

Time complexity: O(n) 
Auxiliary Space: O(n) 

Implementation:

Python3




# Function to create an empty stack. It
# initializes size of stack as 0
def createStack():
    stack = []
    return stack
 
# Function to determine the size of the stack
def size(stack):
    return len(stack)
 
# Stack is empty if the size is 0
def isEmpty(stack):
    if size(stack) == 0:
        return true
 
# Function to add an item to stack . It
# increases size by 1
def push(stack, item):
    stack.append(item)
 
# Function to remove an item from stack.
# It decreases size by 1
def pop(stack):
    if isEmpty(stack):
        return
    return stack.pop()
 
# A stack based function to reverse a string
def reverse(string):
    n = len(string)
 
    # Create a empty stack
    stack = createStack()
 
    # Push all characters of string to stack
    for i in range(0, n, 1):
        push(stack, string[i])
 
    # Making the string empty since all
    # characters are saved in stack
    string = ""
 
    # Pop all characters of string and put
    # them back to string
    for i in range(0, n, 1):
        string += pop(stack)
 
    return string
 
 
# Driver code
s = "Geeksforgeeks"
print("The original string is : ", end="")
print(s)
print("The reversed string(using stack) is : ", end="")
print(reverse(s))

Output

The original string is : Geeksforgeeks
The reversed string(using stack) is : skeegrofskeeG

Method 4: Reverse string in Python using an extended slice

Extended slice offers to put a “step” field as [start, stop, step], and giving no field as start and stop indicates default to 0 and string length respectively, and “-1” denotes starting from the end and stop at the start, hence reversing a string. 

Time complexity: O(n) 
Auxiliary Space: O(1) 

Implementation:

Python3




# Function to reverse a string
def reverse(string):
    string = string[::-1]
    return string
 
s = "Geeksforgeeks"
 
print("The original string is : ", end="")
print(s)
 
print("The reversed string(using extended slice syntax) is : ", end="")
print(reverse(s))

Output

The original string is : Geeksforgeeks
The reversed string(using extended slice syntax) is : skeegrofskeeG

Method 4: Reverse string in Python using reversed() method

The reversed() returns the reversed iterator of the given string and then its elements are joined empty string separated using join(). And reversed order string is formed. 

Time complexity: O(n) 
Auxiliary Space: O(1) 

Implementation:

Python3




# Python code to reverse a string
# using reversed()
 
# Function to reverse a string
def reverse(string):
    string = "".join(reversed(string))
    return string
 
s = "Geeksforgeeks"
 
print("The original string is : ", end="")
print(s)
 
print("The reversed string(using reversed) is : ", end="")
print(reverse(s))

Output

The original string is : Geeksforgeeks
The reversed string(using reversed) is : skeegrofskeeG

Method 5: Reverse string in Python using list comprehension()

List comprehension creates the list of elements of a string in reverse order and then its elements are joined using join(). And reversed order string is formed.

Time complexity: O(n)
Auxiliary Space: O(1) 

Implementation:

Python3




# Function to reverse a string
def reverse(string):
    string = [string[i] for i in range(len(string)-1, -1, -1)]
    return "".join(string)
 
s = "Geeksforgeeks"
 
print("The original string  is : ", s)
 
print("The reversed string(using reversed) is : ", reverse(s))

Output

The original string  is :  Geeksforgeeks
The reversed string(using reversed) is :  skeegrofskeeG

Method 6: Reverse string in Python using the function call

Function to reverse a string by converting string to list then reversed it and again convert it to string.

Time complexity: O(n)
Auxiliary Space: O(1) 

Implementation:

Python3




# Function to reverse a string
# by converting string to list
# then reversed it and again convert it to string
def reverse(string):
    string = list(string)
    string.reverse()
    return "".join(string)
 
s = "Geeksforgeeks"
 
print("The original string  is : ", s)
 
print("The reversed string(using reversed) is : ", reverse(s))
 
# This code is contributed by Susobhan AKhuli

Output

The original string  is :  Geeksforgeeks
The reversed string(using reversed) is :  skeegrofskeeG

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