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

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.