5 Ways to Reverse String in Python

综合编程 2017-12-31

Hello everyone, in this tutorial we’ll see different ways to reverse string in Python.

As we know, we can reverse a list
using reverse()
method but Python doesn’t have the reverse()
method for string.

Here are some alternate and easy ways to reverse a string.

Ways to Reverse String in Python

1. Using Loop

string1 =  "the crazy programmer"
string2 = ""
 
i = len(string1)-1
 
while(i>=0):
  string2 = string2 + string1[i]
  i = i-1
 
print "original = " + string1
print "reverse  = " + string2

Output:

original = the crazy programmer

reverse = remmargorp yzarc eht

In above program, we’ve started a loop from the last index (length-1) to first index (0) of string1. In each step of loop, it will pick the character from right-side in string1 and concatenate with string2.

2. Using Recursion

def reverse_it(string):
  if len(string)==0:
    return string
  else:
    return reverse_it(string[1:]) + string[0]
    print "added " + string[0]
 
string1 = "the crazy programmer"
string2 = reverse_it(string1)
 
print "original = " + string1
print "reversed = " + string2

In above program, there is a reverse_it()
method which accepts a string and then it will check if the string is empty or not, if empty then it will return the string otherwise it will call itself by passing string from its second character to last character.

String = “hello”

Print string[1:]

Output: ‘ello’

After calling reverse_it()
method again and again there will be a point when string will be empty then the condition

if len(string) == 0:

will be true , it will return the string. return
statement will throw the execution, where it came from.

So in

Return reverse_it(string[1:]) + string[0]

the “+ string[0] “
will be executed next, which will add the first letter at last.

3. Using Stack

def create_stack():
  #it will  create a List named as stack and return it
  stack = []
  return stack
 
def push(stack,element):
  #it will add a new element to List
  stack.append(element)
 
def pop(stack):
  #it will delete the last element from  List
  if len(stack) == 0:
    return
  return stack.pop()
 
def reverse(string):
 
  #method to reverse the string using stack's functions
  n = len(string)
  
  #to create a empty list (stack)
  stack = create_stack()
 
  #inserting character of string into List
  for i in range(0,n):
    push(stack,string[i])
 
  #making string empty
  string = ""
 
  #getting last element of the List (stack) and storing it into string
  for i in range(0,n):
    string = string + pop(stack)
  return string
 
string1 = "the crazy programer"
string2 = reverse(string1)
 
print "original = " + string1
print "reversed = " + string2

In above program, we’re using concept of stack having push and pop
functions.

To implement stack concept we’re using list.

When we call reverse()
method, it will create a list
named as ‘stack’ and insert all the characters of string into list using push()
method. At last it will fetch all the elements in the list
from last to first one by one and store them into the string.

4. Using Extended Slice

string = "the crazy programmer"
print "original = " + string
 
string = string[::-1]
print "reversed = " + string

Mostly extended slice is used for skipping the steps but if we put -1 in third ‘step’
or ‘stride’
argument then we can get the reverse of a string, list and tupple.

5. Using List

string = "the crazy programmer"
print "original = " + string
 
#convrting string into list
list1 = list(string)
 
#applying reverse method of list
list1.reverse()
 
#converting list into string
string = ''.join(list1)
print "reversed = " + string

String doesn’t have reverse()
method but lists
have. So we are converting string into list, performing reverse()
operation and again converting it back into string using ‘ ’.join()
method.

Comment below if you have queries or know any other way to reverse a string in python.

The Crazy Programmer

责编内容by:The Crazy Programmer (源链)。感谢您的支持!

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