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Alright, so moving on now with the

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example that we started in the previous

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video. So a generator works like an

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iterator, and what we can do is, we can

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actually use next to get the next value

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instead of using it in a loop, and

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obviously, we used it in a loop in the

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previous video. So what we're going to do

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to see that working, we'll come up here to

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line 17, and actually before line 17,

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we're going to put a print statement in

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there, so let's go ahead and do that. So

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we do print, parentheses next parentheses

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big underscore range. So what we're

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going to do now is delete this line 12

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because we don't need that anymore,

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and by doing that, effectively, line 15

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becomes line 14, so I'm just going to

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change the reference to that so it's

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clear in our code. And of course that code

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we deleted was only there to show that

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my underscore range wasn't called by

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the assignment on line 14. Alright, so

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let's actually run the code, and we can

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see that it stopped on line 14, as we

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would expect it to do. So the next line

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to execute should be our call to next,

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which is currently on line 16, and

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that gets the next value from our

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generator. Now as we haven't used the

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generator yet, the next value is

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currently the first value, so in other

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words we should get zero printed here.

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So press enter and you can see we do get

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zero returned, as well as the message

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that my underscore range starts and

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we're now paused on line 22. So at this

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point before we continue, I've actually

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got a mini challenge for you. I'm not

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going to use a slide, so you can actually

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see the code which is on the screen at

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the moment. So at this point, what will be

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the first value appended to big

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underscore list on line 25? So what will

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be the first value appended to big

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underscore list on line 25, given that we've

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already had a call to the my underscore

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range function. So pause the video, have a

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think about that and see if you can

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figure it out and come back and we'll go

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through the answer.

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Alright, so let's see what happens when

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I press enter to startexecuting the loop.  

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And you can see my underscore range is

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returning one, and we're in line 24, the

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inside loop. So the first value that's going

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to be added to the list is 1, and that's

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because we've already consumed the first

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value from our generator, and we did

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that when we asked for the next value on

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line 16. Now if you recall the discussion

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of iterators in section 7, a for loop is

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just calling next for us. So each time I

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press enter now, the for loop is

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effectively calling next to get the next

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value. Now because the first value's

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already been returned before the loop

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started - I just do this and finish it off -

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we actually only go around four times, as

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you can see there, and the list is

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showing the output, only one, two, three

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and four in this case, instead of the

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zero which it showed last time, prior to

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our changing the code to call the next

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function on line 16. So if you worked out

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that that's what would happen,

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congratulations and well done. Now that

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also explains why it can be a bad idea

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to assign a generator to a variable, and

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that's as we've currently got on line 13 - the

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big underscore range equals

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my underscore range, 5 in parentheses.

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Alright, so at this point we've exhausted

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all the values returned from our my

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underscore range generator. So if we go ahead

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and add some extra code to the program,

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it won't actually do anything. So what

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I'm going to do at this point, is comment

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out all those input lines so we don't

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have to press enter, moving forward,

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so let's go and do that, and I'll indent

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that one. Alright and there's also one on

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line 22 - we'll comment that out as well.

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Right now I've done that, what I'm going

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to do is add some code. I'm going to add

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some code after our prints, right down

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the bottom of the program. So let's

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going to do that, after our print

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big underscore list. So on line 31

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I'm going to do print double quotes

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looping again ... or not.

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Then we're going to do for i in big

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underscore range

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colon, then print parentheses double

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quote i is, then left and right curly

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braces dot format i. Alright, so if I run

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that program now, you can see that

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nothing happens in that final for loop,

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looping again or not. This print isn't

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executed - there's nothing showing on the

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screen and the program has actually

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exited. So storing my underscore range 5

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in big range is fine, if you want to call

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next each time you want a new value, but

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it isn't a good idea if you intend using

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it again in a for loop. So in that case,

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you should just use the my underscore range 5

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method function call direct again.

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So we'd go ahead and change that then -

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instead of for i in big underscore

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range, we change that for i in my

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underscore range, then five in

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parentheses, which is the number we want

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to pass to it. So we're calling the

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function direct. Run that again and you

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can see, in this case now, we're correctly

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getting the output because we're not

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using the variable - rather we're 

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actually using the function call. Alright,

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so the output is now correct and

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returning the right values. Now before I

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finish this video, I should mention that

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range does work if we store it. So I'm

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going to undo that last change that we

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added. Go back to big underscore

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range. Then we're going to go ahead and

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re-enable the code I commented out on line

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12 - big underscore range equals range 5.

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So go ahead and do that, then I'm going

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to comment out the call to our function,

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like so, and now that I've done that,

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I want to actually delete this call,

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this line 16, because we don't want to

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call next on the range object, so I'm

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going to delete that as well. And now

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when we run it, you can see that in both

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cases that's working fine, and the

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range class behaves like an iterable. In

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other words, it's reset each time it's

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used, which wasn't the case when you used

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a variable that actually called the

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function that we actually wrote. So again,

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the range class behaves like an iterable -

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each time it's called,

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it's actually reset. Now here my

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underscore range isn't really very

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useful, other than to show how to write a

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generator, so in the next video we're

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going to look at some more useful

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generators. So I'll see you in that next video.