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So up until now, we learned that strings can be accessed quite easily and using the square brackets,

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we can access different parts of the string.

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And this idea of a start, a stop and a step over is what we call slicing or string slicing, because

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we can slice the string however we like.

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But we also need to learn another important term that's going to come up again and again throughout

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this course.

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And as a matter of fact, it's an important concept that as you get more advanced into programming,

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you really need to understand what is this concept?

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Well, it's this idea of immutability.

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It's an important term in programming.

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What does immutability mean?

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Well, strings in Python are immutable, that means they cannot be changed.

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What I mean by that?

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Now that we've assigned selfish this value, this string, well, I can reassign it, right, I can

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say selfish is one hundred now.

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And if I print selfish.

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And I click, run, that works, but if I instead do something like the first index of selfish is going

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to equal eight and I click run.

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I get an error, I get a type error saying string object does not support item assignment.

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Why is that?

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Because strings are immutable.

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That is, I cannot change the value of this once it's created.

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I can just immediately change it to eight, one, two, three, four, five, six, seven.

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No, it has to stay the same.

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The only way that I can remove this or change this is to completely reassign the value.

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So that in memory, Python removes all of this from our bookshelf of memory and instead just assigns

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eight into the zero bookshelf and removes everything else because we don't use it anymore.

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Now, this idea of immutability is something we'll explore more and more, especially when we start

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talking about lists.

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But for now, just remember that you can't reassign part of a string once created.

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It exists like that in that form.

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The only way we can change it is to create something new.

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We can do selfish plus eight and we can create it that way.

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But now this selfish is a whole new string.

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This no longer exists and a whole new shelf space was created for us to use this whole new string.

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Again, if this doesn't make sense to you or why it's important just yet, don't worry, we'll get there.

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For now, though, I'll see in the next video.

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Bye bye.