Python For Loops

Quick reference

• 00:04 Okay, in this video I want to talk about for loops.
• 00:07 And a for loop is a type of Python loop.
• 00:09 And a loop is exactly what it sounds like, it loops through things.
• 00:13 So we've been talking about lists and tuples.
• 00:15 Those are our lists.
• 00:16 If we want to loop through the list and, for instance,
• 00:19 pull out each item in the list, we could use a for loop for that.
• 00:22 So a lot of times, we're going to be getting data from Excel.
• 00:25 We're going to get them in list form.
• 00:26 And we need to sort of loop through the columns and rows in Excel and
• 00:30 grab different information, different data out of those things.
• 00:34 And a lot of times, we'll use different types of loops.
• 00:37 The most popular is probably the for loop.
• 00:38 So let's go ahead and start out by creating a list called names.
• 00:44 Give us some practice making a list.
• 00:46 So let's go John, Tim, and Mary.
• 00:50 Now, what if we wanted to loop through this thing, and print out each item?
• 00:55 We've already learned that we can print out a single item by calling names, and
• 01:00 then the item number, right?
• 01:01 But how do we print out all the items one at a time,
• 01:04 or do something else with them if we wanted to?
• 01:07 Ultimately, we're going to get data from our Excel spreadsheet because we
• 01:10 want to do something with it.
• 01:12 So how do we do something with that data, with each item of that data?
• 01:15 So that's one of the things we use for loops for.
• 01:17 So to create a for loop, we start out by typing for.
• 01:21 So let's go, for name in names.
• 01:25 Now, you'll notice that this name, where are we getting that?
• 01:28 Well, I just invented it.
• 01:29 We could call this anything we want.
• 01:31 We could call it, for x in names.
• 01:33 We could call it, for pizza in names, anything you want.
• 01:37 But we're going to, these are all, what are these things?
• 01:40 These are names.
• 01:42 So what's the singular of names?
• 01:45 Name, so we're going to get each name from this list of names.
• 01:49 So I just called it name right there.
• 01:51 Now, we put a colon here, and then hit Enter.
• 01:55 Now, notice that the cursor is now right here.
• 01:58 When we hit Enter our Sublime Text editor automatically indents for us.
• 02:04 And indentation in Python is very important, Python is indentation specific.
• 02:09 So to do this, we're not hitting the space bar a bunch of times, don't ever do that.
• 02:13 What you want to do is hit the Tab key on your keyboard, and
• 02:16 you'll notice it just tabs over.
• 02:19 Or if you just come up here and hit Enter, like I said,
• 02:21 Sublime Text will tab it for you.
• 02:23 Now inside of here, we can do anything we want with these names.
• 02:27 So for instance, let's just print out each name.
• 02:30 So I'm referencing this name right here.
• 02:32 So what Python does is it will start at the beginning of this thing, and
• 02:35 it will loop through.
• 02:36 And every time it does, it grabs an item.
• 02:40 And it assigns it to this variable name.
• 02:43 And it loops through again, grabs the next item, assigns that to this variable name.
• 02:49 Then it loops through again, grabs the next item,
• 02:52 assigns it to that variable name.
• 02:54 And then here, and anywhere else below here as long as we're indented,
• 02:58 we can do anything we want.
• 03:00 So all we really want to do right now is just print each of these names.
• 03:03 So let's go ahead, get rid of that line here.
• 03:06 Let's save this and run it, and see what this looks like.
• 03:10 So let's go print.
• 03:11 And you can see, boom, it just prints out John, Tim, Mary, one at a time.
• 03:15 And you'll notice how that's different than if we were just to print out our
• 03:19 whole list as we've done in the past.
• 03:22 If we did that, and came down here and ran this again, you notice in the past,
• 03:26 we got this whole big list, that the items are in quotation marks.
• 03:30 There's this bracket, this is not very useful.
• 03:33 This, on the other hand, is useful.
• 03:36 We're printing out each individual thing, and
• 03:38 we can do anything we want with each of these individual things.
• 03:41 For instance, if we wanted to add a little something else,
• 03:44 we could create something called an f string.
• 03:46 And we really don't care too much what these are.
• 03:48 But inside of here, we can write some text.
• 03:51 So we can go, Hello there.
• 03:54 And then let's put curly brackets, and then we could type in name.
• 03:58 And then we can get rid of this thing.
• 03:59 So this will print out, Hello there name.
• 04:03 And then we can put other things too.
• 04:06 So if we were to save this, and let's get rid of this line.
• 04:09 And save this, head back over to our terminal.
• 04:12 Let's clear the screen and run this guy.
• 04:14 It says, Hello there John.
• 04:15 Hello there Tim, Hello there Mary, and we could do anything we want.
• 04:18 So obviously, this is a very simplistic sort of thing to do.
• 04:23 But in the future, we'll get more complicated with what we want to do with
• 04:27 the things that we're pulling out of our lists.
• 04:29 But this gives us a way to do it.
• 04:31 Now, we can loop through just about anything, right?
• 04:34 Here we're listing through a list.
• 04:36 We can also list through a tuple, the same way.
• 04:38 We could also just create a variable.
• 04:40 Let's call first_name, and set that equal to John.
• 04:44 So here we can go, for letter in first_name.
• 04:52 And then let's just print out letter.
• 04:55 So this will loop through here.
• 04:57 And each of these items, which will be text characters,
• 05:01 it will print out the letter.
• 05:03 So if we save this and run this, you can see one at a time, J-o-h-n.
• 05:09 So loops are very powerful, they're very easy to use.
• 05:13 And this format is sort of important with Python,
• 05:16 where you see you do a thing here, you put a colon.
• 05:19 And then the next line is indented, and
• 05:22 all the lines after this will continue to be indented.
• 05:26 And all of these things will relate to whatever you've done here.
• 05:31 And then as soon as you come outside of here, and
• 05:34 go back to normal indentation like that, then you're breaking out of this for
• 05:39 loop, and no longer doing loopy things.
• 05:42 So very cool and very easy to use.
• 05:44 So that's all for this video.
• 05:46 In the next video, we'll look at random numbers.

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