Python for Beginners, Part 12: Lists of Things

Let's cover the list data structure and why it's so wonderful.In case you missed it, here are the previous parts of the series

• Python for Beginners, Part 1: How to Download and Install Python
• Python for Beginners, Part 2: Hello World Exercise
• Python for Beginners, Part 3: The Turtle Module
• Python for Beginners, Part 4: Interactive Shell vs. Script
• Python for Beginners, Part 5: Variables
• Python for Beginners, Part 7: Fun Fun Functions
• Python for Beginners, Part 8: Function Arguments
• Python for Beginners, Part 9: Loops
• Python for Beginners, Part 10: Primitive Data
• Python for Beginners, Part 11: String Slicing

Transcript

0:00 Hey guys, what's up? 0:01 So in the last video I talked about string slicing. 0:06 In this video I'm gonna talk about lists, okay? 0:08 Lists of things and what the heck are lists. 0:11 Lists are awesome. 0:12 However, in the last video I left you guys with a question. 0:16 I said, take this, 0:20 right, and parse it. 0:21 And basically XBox 360, pull that out, 0:25 save it in a variable like product. 0:27 Pull this out, save it in a variable like price. 0:30 And save this in a variable like condition. 0:32 Right, so when you have your Excel sheet open, 0:35 it looks really nice, it'll look like this. 0:43 My solution, I'm gonna do it in a different way 0:47 because if you try to use it as index, this is the solution. 0:50 So you can pause the video, think about how it works. 0:53 That's how you'll pull the 150 0:55 and using the same logic, you'll pull the New. 0:57 However, index is a very ugly method to use 1:01 for getting, parsing the string. 1:04 What I want to show you guys is this method called find. 1:07 Okay, that's a very nice method. 1:09 Let's say we take the data, and I do data.find 1:14 and find, it shows you the bottom what it takes in 1:17 as the function, it takes in the substring 1:21 and then it takes in optional arguments, like start and n. 1:26 So I'm gonna say data.find 1:29 and I'll give it 1:30 substring pite. 1:33 What a substring means is that, that's something 1:37 that exists in the original string. 1:41 For example, 1:44 I have to give find, 1:45 the function find or the method find, 1:47 I have to give it something that exists within this. 1:50 If I gave it something that doesn't exist within it 1:52 like banana, 1:54 it would say negative one, 1:56 like I didn't find anything. 1:58 But if I gave it a pite, you can see that it finds a nine. 2:04 And another thing you can give it is how you solve... 2:09 Is you can give it where to start from, okay? 2:12 So I can say, for example, 2:15 start looking after ten 2:19 or look for pite, 2:21 but I want you to start at string nine, 2:24 okay? 2:25 Or I want you to start at string ten, alright? 2:29 And now it finds a pite at location 15. 2:32 So if I do data, and if you count it up, 2:35 you'll see that this is the pite 2:37 and it is at indeed at location 15. 2:39 If I do data(15), you'll see that 2:41 it gives you back that pite. 2:45 Right? 2:47 Okay, so by getting that second pite, 2:51 now you can get the value in between the first pite 2:54 and the second pite by saying something like, 2:59 start from finding the first pite 3:03 and then go up to 3:06 finding the second pite. 3:10 Right? 3:11 So I can say, finding, 3:14 or start from, 3:17 or look for pite. 3:19 And then start from ten, for example, right? 3:24 And this gives you this guy here. 3:26 And just to make sure we don't 3:27 include the pite in the first one 3:29 we can just start from plus one with that. 3:31 Okay? 3:32 So that gives you in between the first and the second pite 3:34 you get probably like 150. 3:36 Okay, so, 3:38 the reason why I went even more in depth in strings 3:41 even when the video called lists 3:43 is because a lot of what you learn from strings 3:47 is applicable to lists, okay? 3:49 So, let's take a list and call it groceries. 3:54 And I will have apple, and I foreshadowed this 3:57 for you guys a little bit... 3:59 Banana--and you can also have integers. 4:01 Although usually you try to 4:02 put the same kind of thing in the list. 4:06 But sure, let's put five in there and six in there 4:09 and then oranges or something, okay? 4:12 Cool. 4:13 Now, if I wanna 4:15 take this list 4:17 and I wanna get the first element and the second element, 4:19 if it was just a string, 4:22 right? 4:22 Like the reason why lists are useful is 'cause 4:24 you can use it to store multiple variables. 4:29 Like for example, if you wanted to use variables 4:31 to store this, aww shh-- 4:34 It would be a little... 4:38 It would be weird. 4:39 'Cause you will say groceries, zero is equal to apple. 4:43 You would say... 4:51 Groceries of one are banana. 4:53 And so then when you do groceries of zero, 4:55 you get back apple. 4:57 And when you do groceries of one, 5:00 you get back banana. 5:02 But lists make it, make that thing, 5:05 for you in a really easy way, okay? 5:09 So now, if I do groceries and if I do groceries of zero, 5:14 I get back apple, okay? 5:16 And if I do groceries of one, I get back banana. 5:19 Because apple is in the zero position. 5:22 Banana is in the first position. 5:25 This is in the second, third, fourth position, okay? 5:30 So lists make it really nice for you. 5:33 Imagine if you were trying to store data for a race. 5:36 So like, four of your friends ran really fast 5:40 and you wanted to record who came first, who came second. 5:43 So you can save 5:46 race is equal to 5:49 like John came first, and then Bob came second, 5:53 and then, you know, whatever, like Timothy came in third, 5:59 uh, Timothy is pretty slow. (laughs) 6:03 So we can say like, okay, who came in first? 6:07 We can ask that question. 6:08 We get back John. 6:09 We can say, who came in second? 6:11 We get back Bob. 6:12 And I can say, who came in third? 6:14 Or I can say who came in last? 6:17 That negative one gets you the last element. 6:19 And this answers all my questions. 6:22 So just like how were able to slice strings, 6:26 we're able to slice 6:28 lists, okay? 6:30 But notice, lists is nicer for elements. 6:33 So for example, 6:35 XBox 360 and all this stuff, 6:38 I'll show you guys a really cool trick you can do with lists 6:41 to break that up into pieces. 6:43 So like for example, 6:46 if I gave you a string like this, right, 6:48 what is going on? 6:50 Notice that there are a lot of spaces in between, right? 6:52 Let's just replace those spaces, 6:54 just so it's more visual, 6:56 let's replace those space with that, 6:59 and let's say we want to get the what part separately, 7:02 is part separately, going part separately, 7:04 and on part separately, 7:07 without having any of the dashes in the middle. 7:10 There's a method we can use called .split, okay? 7:14 And we can pass to .split what we want to split by. 7:19 So I can say something like this, 7:21 I want to split by the dashes, okay? 7:23 So check it out, now I got what is going on, right? 7:27 This is a list 7:30 of strings. 7:31 Now the data complexity is getting a little bit higher, 7:34 it's a list containing strings inside of it. 7:39 Okay, so, I can call this like, 7:43 you know, 7:46 greeting or something, it doesn't matter, 7:48 and if I do greeting, I can say 7:50 What's the first word of greeting? 7:53 What's the second word? 7:58 Whoops. 8:02 Greeting, right, what's the second word? 8:05 And for example, I can say what's the last word? 8:09 And it'll give me what is going on, 8:11 on being the last word, right? 8:13 Now, I can also do string slicing just like 8:17 how I can do in strings. 8:19 So I have start, I have stop, 8:22 and I have step. 8:24 So if I take the race one again, 8:27 I can say go from zero all the way to the end. 8:31 I can say the same way, like this, 8:35 this is like optional, right? 8:38 It starts with zero and it ends at zero, 8:40 or ends at the last one by default. 8:43 If I wanna get from John to Bob, 8:46 I can say like give me the 8:47 first two... 8:50 first two contestants of the race. 8:53 And it will give me John and Bob. 8:55 Or I'll say give me everybody but the last guy 8:58 so I can ask that question to my list, just like that. 9:04 Okay, now to answer your guys' question 9:06 of how to reverse the string, 9:08 it's the same you can reverse the list as well. 9:12 So, lemme show you guys. 9:14 There are a couple of different ways, 9:15 but I'm gonna show you guys the nicest, the fanciest way. 9:20 So let's take this list 9:23 and I wanna step by... 9:26 Sorry, I wanna start at the default, which is zero. 9:29 I don't have to write zero, 9:30 but I'll just write it for you guys. 9:32 I want to go all the way to the end 9:34 and I don't have to write this, okay? 9:36 So I'll just leave it blank here. 9:39 And for the last part, for step, 9:42 instead of saying step by one, 9:44 which will just give me the whole thing. 9:47 Instead of saying give me every other element, 9:49 so like give me John and then Timothy 9:52 I will say 9:55 step by negative one. 9:57 So check this out, 10:00 let's remove 10:03 this, 10:05 right? 10:06 And let's remove that guy, and let's do that, 10:09 and you will see how it steps. 10:14 It just reversed the list. 10:17 If we have 10:18 the same string, like 10:20 let's say we have data I can do the same way and 10:25 reverse everything in data. 10:28 So you can see XBox 360 and New and 150 10:31 are all written backwards, okay? 10:35 So that's how you would like reverse something. 10:38 Now I want to talk about 10:43 split again, 10:44 and I want to talk about one very important method 10:48 called a pen for a list. 10:50 One of the most commonly used things 10:53 that any programmer does in any language, okay? 10:57 So split is like Java, Cs, everybody uses that. 11:01 It just might not be called split. 11:02 And the same thing in Python, everybody uses split 11:05 and the next method I'm about to show you, pen. 11:07 Very common for all the games you make, 11:10 for everything that you do, it's going to be like 11:11 one of the most common thing you use, 11:13 especially a pen, so pay attention. 11:15 So I'm gonna show you 11:18 the method called 11:20 the split, okay? 11:22 So I've shown you a little bit of that already. 11:23 So let's say I take data and I wanna break it up, 11:27 right, product, price, condition. 11:31 Very easy way to do it, very easy way to do it split. 11:33 So let's use data.split, 11:36 and I wanna say split by 11:39 pite. 11:41 Boom, look at that. 11:42 How nice is that, right? 11:44 It automatically just split it by that 11:46 and you can store that in 11:50 details or something. 11:52 And now if I do details of zero, 11:57 and I can set that equal to product. 12:00 So now if I do product, I get that. 12:03 I can say 12:05 price is equal to 12:07 details 12:09 of one 12:10 and I can say condition 12:13 is equal to details 12:14 of two. 12:16 Okay, price, condition, 12:19 boom, 12:20 okay? 12:21 So that was like some really nice ways to get this done. 12:24 In the next video I will talk about a pen. 12:27 So stay tuned.