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

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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 we

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can slice the string.

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However we like but we also need to learn another important term that's going to come up again and again

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throughout 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 you

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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 well strings in Python are immutable.

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That means they cannot be changed.

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What I mean by that now that we've assigned selfish this value this string.

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Well I can reassign it right.

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I can say selfish is a hundred now and if I print selfish and I click Run that works but if I instead

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do something like the first index of selfish is going to equal 8 and I click Run I get an error I get

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a type error saying String object does not support item assignment why is that.

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Because strings are immutable.

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That is I cannot change the value of this.

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Once it's created I can't just immediately change it to eight.

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One two three four five six seven.

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No.

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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 so that in memory

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Python removes all of this from our bookshelf of memory and instead just assigns eight into the zero

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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 talking

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about lists.

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

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Once created 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 8 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 again.

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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 by.