Bummer! This is just a preview. You need to be signed in with a Basic account to view the entire video.
Iterating with Ranges4:07 with Ashley Boucher
Another iteration technique that Pythonistas can use is iterating with ranges.
Welcome back. 0:00 Now that we've tackled enumeration, we'll spend this video talking about ranges. 0:02 Ranges are how we iterate over numbers in Python. 0:06 They're commonly used when you wanna repeat a behavior a certain number 0:09 of times. 0:12 But this behavior's not necessarily tied to elements of a sequence. 0:13 In fact, iterating over Python ranges is very analogous to the traditional for 0:16 loops you'll find in other programming languages. 0:20 Let's say we wanted to have a for loop that loops ten times. 0:23 Knowing what you know so far about iteration, 0:26 you might try something like this. 0:29 Let's see what happens when I run this. 0:37 Okay, we're getting a TypeError here. 0:46 It says, 'int' object is not iterable. 0:48 This is telling us that 10 is an int, or integer, and it's not iterable. 0:51 It's not a sequence, so we can't loop over it like we would a list, 0:55 a tuple or a string. 1:00 So what do we do? 1:01 We use a range. 1:02 Ranges are the Python way of creating an ordered, iterable sequence of numbers 1:04 with a starting number, stopping number, and a step, or increment value. 1:08 Range is a Python method, like enumerate. 1:13 It takes three arguments, start, stop, and step. 1:15 Start is the starting index. 1:19 In other words, at what integer should the range begin? 1:20 The default value is 0. 1:24 Stop is the ending index, the number at which the range ends, 1:25 you must specify this value. 1:29 It's important to note that ranges are exclusive of the stop value. 1:31 Finally, step represents how much the index increases or 1:35 increments from the previous number. 1:39 The default is 1. 1:40 Let's start exploring a range here in Workspaces. 1:42 Feel free to follow along with me. 1:44 You'll have an opportunity to try on your own in just a little while. 1:46 We'll pick up from our previous example. 1:49 To iterate over the numbers 1 through 10, 1:51 we'll change this incorrect code to use a range instead. 1:53 0 is our start value, 10 is our stop value, and 2:02 1 is our step or increment value. 2:06 Let's save and run this. 2:09 You can see that the code printed out all the numbers between 0 and 9, but 2:15 it didn't print 10. 2:19 Well, why is that? 2:20 It's because ranges are exclusive of stop values. 2:22 Meaning the sequence returned from our call to the range function began at 0 and 2:24 each element in the sequence increased by one, stopping right before it got to 10. 2:29 But because the range began at 0, it still looped 10 times. 2:33 This syntax for this example is a little verbose. 2:37 Luckily, Python is smart enough to make a lot of assumptions on our behalf. 2:40 When it comes to ranges, Python will always assume that we want the sequence to 2:43 start at zero and increase by one unless we tell it otherwise. 2:47 This means that the example we just wrote can be shortened to this. 2:52 When you create a range, feel free to only pass the stop value unless you need 3:00 a start or a step value that defers from the default. 3:04 For instance, say we wanted this range to start at 5 instead of 0. 3:07 In that case, we would again have to pass a start value before the stop value. 3:11 I've left out the step value here because I'm fine with using the default of 1. 3:19 Let's see what this looks like. 3:23 Cool, all right, take a moment here to try this on your own, 3:31 pause the video after these instructions. 3:34 Open the attached workspace and down in the terminal, 3:36 iterate over a range that starts and ends at any two numbers of your choosing. 3:39 Then take some time to change the start, stop and step values and see what happens. 3:43 For example, what happens if the start and stop value are the same? 3:49 What if the step value is two or five instead of one? 3:53 What if the start value is higher than the stop and 3:56 the step value is a negative number? 3:59 When you've taken time to play around with ranges, 4:02 come join me in the next stage to learn about sequence operations. 4:04
You need to sign up for Treehouse in order to download course files.Sign up