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Python has several sequential types that look like lists of things,

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and we're going to look at a few of them right now.

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Let's make a working copy of variables.py and we'll call this variables-lists.py.

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And we'll open that working copy.

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So let's create a variable.

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And we'll just call it x. And we'll assign it a list of values in

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parentheses (1, 2, 3).

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And we'll go ahead and we'll print(x).

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What print will do with this is it will try to print it in a way that Python

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could actually create one if it needed to.

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And so it has it in the parentheses just like that.

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So let's print the type of it, also.

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Save that and run it.

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So the class is tuple.

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So this is a tuple.

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And a tuple is created with parentheses.

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And a tuple is an immutable object.

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So I can't insert things.

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I can't append things. I can't delete things.

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Once I've created it, I've created it.

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And I can't change it.

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So this is useful for a lot of stuff.

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Perhaps you just to operate on a fixed list of things.

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In fact, most of time, when you need a list of something, you're probably not

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going to need an immutable list.

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And to use a tuple is going to be faster than to use immutable list.

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On the other hand, if we create this with the square brackets, then we get the list type.

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I'll save this and run it.

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And the list type is mutable.

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I can, in fact, add something to the end of it.

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I can say x.append and call it the number 5,

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and save that and run it,

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and now we have the number 5 at the end. Or I can say x.insert,

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and insert it at the beginning, which I use the index 0 for the beginning, and put a 7 there,

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and save that and run it,

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and now I have a 7 at the beginning.

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I could, of course, insert that at any point.

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If I say 2, use the number 2 there.

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So this is item 0 and this is item 1 and this would be item 2.

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And we can expect the 7 to show up in there.

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So I'll save it and I'll run it.

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And there we have the 7 in there.

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So you can actually modify the list that is mutable, but if I were to change

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this back to the tuple type, which is immutable, and save it and run it, then I get an error.

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That tuple object has no attribute append, and in fact it has no attribute insert

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either, because it's immutable.

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And it cannot be changed.

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So we'll go ahead and we'll take these out.

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And I'm going to show you one other sequence type that you've seen before, but

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you might not have thought it in this way.

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And that is the string.

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If I save this and run it,

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we'll see that we have a string.

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Just like with any sequential type, I can actually look at particular elements

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of the string by subscripting it to say 2.

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So that will be 0, 1, 2.

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I'll just get the r. Save that and run it.

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And there's the r. Or I can do what's called a slice.

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And we'll learn more about slices later on. I can say 2:4.

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And I'll get a slice of just the r and the i. And in slices, it's worth noting

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that even though I'm using the 2 index for the beginning, which would be 0, 1, 2,

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that's the r, that I'm using the 4 index for the end which would be 2, 3, 4, it would be the n.

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The way slices work in Python, they don't actually return that last element.

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And there are explanations in the documentation just to why that is.

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And we will get more into slices in more detail in a later chapter.

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It's also notable that all of these sequence types can be used as iterators.

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So if I go back to (1, 2, 3, 4, 5), I have an immutable tuple.

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And I'm going to for I in x: print(i).

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And so that will print each one on a separate line, each of the

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different elements.

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And in fact, the string also works like that.

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If I put a string in here and save and run, I get each of those individual

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letters from the string.

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So this is how you use sequences in Python.

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There are a number of them.

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These are the most common.

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The tuple is immutable.

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the list is mutable and is designated with the square brackets instead of the

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parenthesis for the tuple,

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and a string is also a sequence, an immutable sequence.