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Iterating with Ranges
4:07Another iteration technique that Pythonistas can use is iterating with ranges.
Welcome back.
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Now that we've tackled enumeration, we'll
spend this video talking about ranges.
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Ranges are how we iterate
over numbers in Python.
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They're commonly used when you wanna
repeat a behavior a certain number
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of times.
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But this behavior's not necessarily
tied to elements of a sequence.
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In fact, iterating over Python ranges is
very analogous to the traditional for
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loops you'll find in other
programming languages.
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Let's say we wanted to have a for
loop that loops ten times.
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Knowing what you know so
far about iteration,
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you might try something like this.
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Let's see what happens when I run this.
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Okay, we're getting a TypeError here.
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It says, 'int' object is not iterable.
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This is telling us that 10 is an int,
or integer, and it's not iterable.
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It's not a sequence, so we can't
loop over it like we would a list,
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a tuple or a string.
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So what do we do?
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We use a range.
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Ranges are the Python way of creating
an ordered, iterable sequence of numbers
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with a starting number, stopping number,
and a step, or increment value.
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Range is a Python method, like enumerate.
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It takes three arguments,
start, stop, and step.
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Start is the starting index.
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In other words,
at what integer should the range begin?
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The default value is 0.
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Stop is the ending index,
the number at which the range ends,
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you must specify this value.
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It's important to note that ranges
are exclusive of the stop value.
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Finally, step represents how
much the index increases or
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increments from the previous number.
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The default is 1.
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Let's start exploring
a range here in Workspaces.
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Feel free to follow along with me.
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You'll have an opportunity to try
on your own in just a little while.
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We'll pick up from our previous example.
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To iterate over the numbers 1 through 10,
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we'll change this incorrect
code to use a range instead.
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0 is our start value,
10 is our stop value, and
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1 is our step or increment value.
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Let's save and run this.
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You can see that the code printed out
all the numbers between 0 and 9, but
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it didn't print 10.
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Well, why is that?
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It's because ranges
are exclusive of stop values.
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Meaning the sequence returned from our
call to the range function began at 0 and
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each element in the sequence increased by
one, stopping right before it got to 10.
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But because the range began at 0,
it still looped 10 times.
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This syntax for
this example is a little verbose.
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Luckily, Python is smart enough to make
a lot of assumptions on our behalf.
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When it comes to ranges, Python will
always assume that we want the sequence to
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start at zero and increase by
one unless we tell it otherwise.
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This means that the example we just
wrote can be shortened to this.
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When you create a range, feel free to
only pass the stop value unless you need
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a start or
a step value that defers from the default.
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For instance, say we wanted this
range to start at 5 instead of 0.
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In that case, we would again have to pass
a start value before the stop value.
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I've left out the step value here because
I'm fine with using the default of 1.
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Let's see what this looks like.
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Cool, all right, take a moment
here to try this on your own,
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pause the video after these instructions.
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Open the attached workspace and
down in the terminal,
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iterate over a range that starts and
ends at any two numbers of your choosing.
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Then take some time to change the start,
stop and step values and see what happens.
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For example, what happens if the start and
stop value are the same?
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What if the step value is two or
five instead of one?
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What if the start value is
higher than the stop and
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the step value is a negative number?
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When you've taken time to
play around with ranges,
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come join me in the next stage to
learn about sequence operations.
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