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Reverse string in Python (6 different ways)

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  • Difficulty Level : Easy
  • Last Updated : 23 Jun, 2022

Python string library does’nt 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. 
 

Using loop

 

Python3




# Python code to reverse a string
# using loop
 
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

Explanation : In above code, we call a function to reverse a string, which iterates to every element and intelligently join each character in the beginning so as to obtain the reversed string. 

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

Using recursion

 

Python3




# Python code to reverse a string
# using recursion
 
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

Time complexity : O(n) 
Auxiliary Space : O(n) 
Explanation : In the above code, 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. 
 

Using stack

 

Python3




# Python code to reverse a string
# using stack
 
# 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

Time complexity : O(n) 
Auxiliary Space : O(n) 
Explanation : An empty stack is created. One by one characters of string are pushed to stack. One by one all characters from stack are popped, and put them back to string. 
 

Using extended slice syntax

 

Python3




# Python code to reverse a string
# using extended slice syntax
 
# 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

Time complexity : O(n) 
Auxiliary Space : O(1) 
Explanation : 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 end and stop at the start, hence reversing string. 
 

Using reversed

 

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

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

Using List-Comprehension

Python3




# Python code to reverse a string
# using list comprehension()
 
# 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

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

Or you can do that (easy-to-understand),

Python3




# Python code to reverse a string
# using list comprehension()
 
# Function to reverse a string
# by coverting 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

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

Explanation: List comprehension create the list of elements of string in reverse order and then its elements are join using join(). And reversed order string is formed.

This article is contributed by Manjeet Singh. If you like GeeksforGeeks and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to review-team@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.


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