Join us and get access to hundreds of tutorials and a community of expert Pythonistas.

Unlock This Lesson

This lesson is for members only. Join us and get access to hundreds of tutorials and a community of expert Pythonistas.

Unlock This Lesson

Hint: You can adjust the default video playback speed in your account settings.
Hint: You can set the default subtitles language in your account settings.
Sorry! Looks like there’s an issue with video playback 🙁 This might be due to a temporary outage or because of a configuration issue with your browser. Please see our video player troubleshooting guide to resolve the issue.

Modifying Strings

Give Feedback

Strings are immutable, meaning they can’t be modified. In this lesson, you’ll learn how to accomplish changing strings by generating a copy of the original string instead:

>>> s = 'mybacon'
>>> s[2] = 'f'
Traceback (most recent call last):
  File "<input>", line 1, in <module>
    s[2] = 'f'
TypeError: 'str' object does not support item assignment

Here’s how to copy a string:

>>> s = 'mybacon'
>>> s = s[:2] + 'f' + s[3:]
>>> s
>>> s = 'mybacon'
>>> s = s.replace('b', 'f')
>>> s

00:00 So, how about modifying strings? Well, basically, you can’t. Strings are immutable.

00:08 Many of the data types you’ve probably seen so far are immutable. Let’s look at this and practice. So, how about a statement like this. Create a string—stick with the string you used earlier, 'mybacon'.

00:20 What if you went to one of the indexes, like let’s say index 2, which would be the letter 'b', and you tried to change it to an 'f'?

00:30 You’ll see that string objects don’t support item assignment. You can’t change the contents—in this case, the single character of the string. It’s immutable. You’d get an error.

00:41 So what if you do want to change it? One of the best answers is making a copy instead. So, to try this out, you’re going to generate a copy of the original string that has the desired change in place. And there’s many ways to do this.

00:56 Here’s one way. If you were to take and reassign s, and you could change up to 2, but not including 2, add a new letter you wanted to add,

01:11 and then tack on the rest of the string, you’d get the same result. In fact, there’s a much simpler way to do this with one of the built-in string methods.

01:20 It’s known as .replace(). If you wanted to change it to 'myfacon', you would just say s = s.replace() and then choose a letter—in this case, 'b' is going to change to the letter 'f'. So, you’re not changing the original string.

01:39 You’re returning from a method a copy of the original object with some of it altered, and assigning it to a new object. In this case, you’re reusing the s object name, but it is a new object.

01:53 The entirety of Section 2 is all about methods that can be applied to strings, and an overview is next.

ugur on Jan. 27, 2021

It seems that you are big fan of bacon. Don’t you? I strongly suggest you that use a different word something sound nice.

Bartosz Zaczyński RP Team on Jan. 28, 2021

@ugur It’s a long-standing tradition in Python to use names such as spam, ham, egg, or bacon for metasyntactic variables instead of the boring ones like foobar. It’s a reference to a Monty Python comedy sketch entitled Spam. So, I suggest that you start liking bacon 😉

Become a Member to join the conversation.