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
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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
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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
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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
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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
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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.
Beginner here, why does [::-1] make it reversed? I tried looking it up but cant find any meaning on the double colon.