#100DaysOfCode in Python Transcripts
Chapter: Days 19-21: Iteration with itertools
Lecture: Iteration Refresher
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All right, so let's discuss what iteration is in Python.
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When we say something is iterable, we're saying
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that you're able to iterate over it,
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you're able to move through it one item by item, okay?
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So the easiest way to demonstrate this
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is just to get a simple list.
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So we'll create a quick list here of numbers.
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Let's go with the numbers 1 through 10.
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Okay, oops, what am I doing?
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1 through 10.
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And we know that,
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and we know that number is 10 digits, right?
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Nice and easy.
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Now if we're iterating over that,
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we're going to run a full loop, so for i in numbers,
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in number, I should say, print i.
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This is something we've all done before, we all know
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what this is, but what's happening behind the scenes?
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Okay, yes we're running a full loop,
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but really what is that full loop doing
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to iterate over the number list
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and give you the numbers?
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Well, it's actually calling the iter dunder method,
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or iter protocol, okay?
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So we can see this if we actually
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drill in to the number list.
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We can see that it is actually calling iter
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or it's capable of being iterated over.
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Okay, so we've got iter and dur number
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and we get true, so it's in there.
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This is an iterable item, we can iterate over it, okay?
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Now another way to demonstrate
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an iterable item is to use next.
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We've all seen next before, or hopefully you've seen next.
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And what happens is when you run next on an iterator,
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when it finishes iterating over the sequence,
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over the list or the string or whatever it happens to be,
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when it finishes this, it then gives you an error,
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okay, it gives you a StopIteration error
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because it's only going to iterate through it
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up until the end and then it will stop.
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So now that we know that iter is actually
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what's being called in the background, we can use that,
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okay, we can use that with next.
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Now if you haven't heard of next,
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next is a little function you can run against an iterator.
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And what it will do is it will pass over,
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it will iterate over that iterator,
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that list or that string or whatever it is,
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and it will continue through it until it hits the end.
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When it hits the last item, when it hits the last character,
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it will actually give you a StopIteration error, okay?
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So we'll demonstrate that with a string called,
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let's call it string, okay?
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So it equals iter, we're actually
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calling iter now over the word string.
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Okay, so we know that when you iterate
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over this word here, over this string,
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you're going to get the letters one by one, right?
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So if we call next on that, we'll get the letter S, okay?
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Now let's copy and paste this a few times,
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just so we can demonstrate.
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We get the T, we get the R, I, N, G.
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But then, when we run it one more time,
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we get the stop iteration, okay?
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And that is because we're calling next directly.
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That's because it's hit the end and it's taken care of.
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It gets to the end but then it's not going to go any further
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because it knows it's already finished.
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Now, when you run a full loop,
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so for character in string,
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print character,
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we get the letters, but we don't get this error,
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we don't get the StopIteration error,
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and that's because it's actually built in to the full loop
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so that it's not going to give you that error.
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It's expected, okay, so it knows
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that it's hit the end and it's not going to actually
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sit there and give you the error.
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And that's it, that's a basic coverage of iteration.
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You see it's just going through each object,
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each item, one by one, to get to the end.
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Now, there is iter tools, a nice series of functions
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that are just so cool and make iteration
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a lot more interesting and a lot easier,
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so that's what we're going to look at.
