WEBVTT

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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 use 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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in print in parenthesis next parenthesis

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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 laps so it's

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clearly 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 count 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 to

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generating 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 append it to bigger

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than school list on line 25? So what we

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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 mu 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 answers.

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Alright so let's see what happens when

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I press enter the static we can delete

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and you can see my underscore ranges

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returning one and we're in line 24 the

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inside loop, so the first value is 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 when 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 values

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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

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

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big underscore range equals

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1 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 minor

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score range generator, so we come ahead

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and add some extra code to the program

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and why don't you 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 it out as well.

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Right now we'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 write down

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the bottom of the program so that's

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going to do that after our print

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big underscore list, so line 30

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what 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 the 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

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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 - core 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 a variable rather were you'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 we

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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 then back to 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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Now 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 and

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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 then

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when you 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 interval 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 call,

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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 we'll see you in that next video.