Welcome back.

Now that we've tackled enumeration, we'll spend this video talking about ranges.

Ranges are how we iterate over numbers in Python.

They're commonly used when you wanna repeat a behavior a certain number

of times.

But this behavior's not necessarily tied to elements of a sequence.

In fact, iterating over Python ranges is very analogous to the traditional for

loops you'll find in other programming languages.

Let's say we wanted to have a for loop that loops ten times.

Knowing what you know so far about iteration,

you might try something like this.

Let's see what happens when I run this.

Okay, we're getting a TypeError here.

It says, 'int' object is not iterable.

This is telling us that 10 is an int, or integer, and it's not iterable.

It's not a sequence, so we can't loop over it like we would a list,

a tuple or a string.

So what do we do?

We use a range.

Ranges are the Python way of creating an ordered, iterable sequence of numbers

with a starting number, stopping number, and a step, or increment value.

Range is a Python method, like enumerate.

It takes three arguments, start, stop, and step.

Start is the starting index.

In other words, at what integer should the range begin?

The default value is 0.

Stop is the ending index, the number at which the range ends,

you must specify this value.

It's important to note that ranges are exclusive of the stop value.

Finally, step represents how much the index increases or

increments from the previous number.

The default is 1.

Let's start exploring a range here in Workspaces.

Feel free to follow along with me.

You'll have an opportunity to try on your own in just a little while.

We'll pick up from our previous example.

To iterate over the numbers 1 through 10,

we'll change this incorrect code to use a range instead.

0 is our start value, 10 is our stop value, and

1 is our step or increment value.

Let's save and run this.

You can see that the code printed out all the numbers between 0 and 9, but

it didn't print 10.

Well, why is that?

It's because ranges are exclusive of stop values.

Meaning the sequence returned from our call to the range function began at 0 and

each element in the sequence increased by one, stopping right before it got to 10.

But because the range began at 0, it still looped 10 times.

This syntax for this example is a little verbose.

Luckily, Python is smart enough to make a lot of assumptions on our behalf.

When it comes to ranges, Python will always assume that we want the sequence to

start at zero and increase by one unless we tell it otherwise.

This means that the example we just wrote can be shortened to this.

When you create a range, feel free to only pass the stop value unless you need

a start or a step value that defers from the default.

For instance, say we wanted this range to start at 5 instead of 0.

In that case, we would again have to pass a start value before the stop value.

I've left out the step value here because I'm fine with using the default of 1.

Let's see what this looks like.

Cool, all right, take a moment here to try this on your own,

pause the video after these instructions.

Open the attached workspace and down in the terminal,

iterate over a range that starts and ends at any two numbers of your choosing.

Then take some time to change the start, stop and step values and see what happens.

For example, what happens if the start and stop value are the same?

What if the step value is two or five instead of one?

What if the start value is higher than the stop and

the step value is a negative number?

When you've taken time to play around with ranges,

come join me in the next stage to learn about sequence operations.