How to reverse string python

21.08.202221.08.2022 admin 0 Comments how, how to made, как, как сделать, как создать, совими руками

How to reverse string python

Reverse string in Python (6 different ways)

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:

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

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)

How to Reverse String in Python

Introduction

Although it may not be a common thing to do in any real-world scenario, reversing strings is a pretty common operation you’ll face in a job interview. Especially if you are applying for a job in a programming language that doesn’t have built-in methods for reversing strings. By asking you to reverse a string, an interviewer can get a pretty accurate impression of how you approach analyzing the problem and building a solution from scratch.

Also, since there can be plenty of solutions for this problem, this is your chance to shine and show your awareness of the different execution speeds between different algorithms, thus create the best possible solution.

In this article, we’ll take a look at how to reverse a string in Python. We’ll consider several possible solutions and compare them, so you can choose the one that best fits your needs.

Strings in Python

Note: The actual object used to deal with strings in Python is called the str object. It essentially represents a string data type.

Reversing a String in Python

Using join() and reversed()

First of all, reversed() returns a reversed iterator for the string passed as its argument. That enables us to go over the original string backward and append its characters to the empty string using str.join() function:

This will create a reversed copy of the original string:

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Using a for Loop

Note: Notice how we’ve been adding each character to the reversed string, but strings in Python are immutable. We can do that because Python, essentially, creates a modified copy of a string each time we append a character to it, before solidifying the result as an immutable string and returning it.

An alternative approach is to iterate over the original string forwards, from the start to the end, and create the reversed version of the original string in the loop itself:

This will give us the same result as using the reversed iterator in the loop.

Using a while Loop

Another loop we can use to reverse a string is the while loop. This approach is a bit more complicated than others, but can give you a great insight in how reversing string works on a lower level:

Which will result in:

Conclusion

How do I reverse words in a string with Python

I am trying to reverse words of a string, but having difficulty, any assistance will be appreciated:

What I get now is: eman ym si tahw

However, I am trying to get: tahw is ym eman (individual words reversed)

12 Answers 12

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Since everyone else’s covered the case where the punctuation moves, I’ll cover the one where you don’t want the punctuation to move.

Breaking this down.

re is python’s regex module, and re.sub is the function in that module that handles substitutions. It has three required parameters.

The second is either a string to substitute in, or a function that takes in a re.MatchObject and outputs a string. I’m using a lambda (or nameless) function that simply outputs the matched string, reversed.

The third is the string you want to do a find in a replace in.

The built-in reversed outputs a reversed object, which you have to cast back to string, so I generally prefer the [::-1] option.

How to Reverse a String in Python

Learn how to reverse a String in Python.

There is no built-in function to reverse a String in Python.

Example

Reverse the string «Hello World»:

Example Explained

We have a string, «Hello World», which we want to reverse:

The String to Reverse

Create a slice that starts at the end of the string, and moves backwards.

Slice the String

Now we have a string txt that reads «Hello World» backwards.

Print the String to demonstrate the result

Print the List

Create a Function

If you like to have a function where you can send your strings, and return them backwards, you can create a function and insert the code from the example above.