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Alright so let's continue with our
ranges.py program, to look at a few

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more things we can do with ranges. If
you want to use a range just to repeat a

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block of code a certain number of times,
then there's no need to provide a start

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value. If you don't provide a start value,
it defaults to zero. So I'm going to

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change the code there and delete the
comma 16 so we've just got 10 in

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parentheses, and if we run the program
now, you can see the program has actually

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gone through 10 times, 0 down to 9. Now we get
the values from 0 to 9 because the start

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value defaults to zero and obviously
it's not included on line 1. So what else

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can we do? Well we can provide a step
value to our ranges. If we do that, we

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have to specify a start as well.
Otherwise, if we try and add just a

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step to our existing code, comma 2,
Python then interprets what I've typed

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as starting at 10 and going up by 2. The
default step value is 1 and you can't

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count from 10 to 2 in steps of 1 and
expect to get any values. So if we run

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the program as is, we get no output at
all on the screen. So to get the values

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from 0 to 10 in steps of 2, because we're
using steps, we have to specify a start

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value and I'm going to enter the value 0
here. So 0 comma 10 comma 2 and now if we

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run that, you can see it gives us the
values we wanted - 0 2 4 6 8. Note that

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we didn't get 10 printed out. If you
recall, ranges go up to but not including

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the stop value, just like slices and as
we discussed in the previous video. Now

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if you want to count backwards, you can
use a negative step range. So what we

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need to do then, because we're going
backwards we'll need to swap the

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start and end. So we're going to start at
10, go down to 0 and the step is going to

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be a minus number, minus 2. If I do that
now and run it, you can see we get the

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values 10 8 6 4 2. So the start value has
to be greater than the stop value when

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using a negative step, for obvious
reasons. For the same reason as we didn't

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get 10 in the previous output when we were
stepping up, we don't get 0 when using a

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negative step. Alright so that's an
introduction now to

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range class. We haven't created very
exciting code here but we've seen how to

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create ranges of values to iterate
over. Now something else you can do with

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a range, is check if a value is in it.
Let's open the conditions.py program

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from a previous video that we've worked
on. You can see it here, conditions.pi,

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so I'm going to open that up. Alright, so there's
our code from that program. Now on line 4

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we're checking to see if age is between
16 and 65 inclusive. We could use a range

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instead. Now I'm not saying that you
should use a range here and the current

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code is the most efficient way of
performing that test, but let's see how

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to do the same thing using a range. So
I'm going to comment out that first line,

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line 4. I'm gonna replace it with if age
in range, and in parenthesis 16 comma 66

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right parenthesis and a colon. Because
the last value isn't included in a range,

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I had to use 66 as the stop value rather
than 65. So let's run the program to

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confirm that it still works: How old are
you? Let's test another, 16 first, Have a

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good day at work.
Run it again, we'll try it with 65.

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That works okay. Run it again, this time with 15,
Enjoy your free time, and one more time,

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we'll try it with, say, the value 75.
So clearly that's working as it should.

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So you saw that I tested it with the, with
a variety of values to make sure it's

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okay. So make sure you do that whenever
you're testing your programs, to make

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sure you're actually getting a proper and
comprehensive test and obviously I could

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do a lot more testing, but we've done a
basic amount of testing to confirm that

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the codes are working pretty well as it
should. Now as I mentioned previously,

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the code that's now commented out on
line 4 is more efficient, but testing

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if a value is in a range can be useful,
and for that reason I've demonstrated

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how to do that. Alright, so I'm going to stop
the video here. In the next one, we'll

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start looking at nested for loops.
See you in the next video.