Python for Beginners, Part 11: String Slicing

Now let's talk about string slicing.

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

Transcript

0:00 There my beautiful children,

0:01 in this video we're gonna talk about string slicing.

0:04 What is string slicing?

0:06 We're not talking about cake slicing, so let's get started.

0:09 Well a string as you remember

0:11 was that thing in the green here,

0:13 but that's just really specific

0:15 to the IDE that we're using,

0:17 if you're using any other text editor it's not necessarily

0:19 gonna be green.

0:20 So the string is just something in quotes.

0:22 Either it's single quotes or double quotes

0:24 as long as it's consistent,

0:27 Can't have a single quote ending with a double quote.

0:30 They gotta match.

0:32 Okay.

0:34 So we have to match with the quotes,

0:37 that's your string, right.

0:39 So what we want to do now is slice those strings.

0:43 Well, what does that mean?

0:46 Imagine I gave you an email address.

0:48 Email is equal to, I don't know,

0:52 rafeh at gmail dot com,

0:56 something like that.

0:57 Well, a common thing that people have to do when they

1:00 are getting this data back is,

1:03 well, this is the username or something,

1:08 this part is the Gmail thing,

1:13 and then this is the dot com part, right.

1:16 So like, let's say we just want the domain or whatever,

1:19 and here we simply want like the username.

1:22 So how would we do that?

1:24 Well, we can use a little bit of string slicing.

1:27 So let's just start with a simple example.

1:29 Let's take hello, and let's say we want to get the first

1:32 Let's take hello, and let's say we want to get the first

1:35 letter from hello, we wanna get just the H.

1:38 Well, how you do it is you index by opening a bracket,

1:42 and closing a square bracket.

1:44 And if I do zero, it'll get me

1:48 the first letter of that, okay.

1:51 So H in this case is zero, right.

1:53 So H in this case is zero, right.

1:55 The E is one, in Python most of the things start from zero.

1:59 So we go all the way up to this O here,

2:02 which is a four, okay.

2:07 So we take this hello and

2:12 whoops

2:13 let's take this hello and let's simply do a 1,

2:16 let's take this hello and let's simply do a 1,

2:19 and that'll give me the E, okay.

2:21 Now another thing I want to show you guys in string slicing,

2:24 besides doing, okay that index,

2:27 right, this passing in the index one,

2:31 will give me the second letter.

2:32 What if we want to do something cooler

2:33 like get a chunk of code?

2:36 Well, how indexing works is it's start, colon stop.

2:39 Well, how indexing works is it's start, colon stop.

2:43 Okay, colon stop.

2:46 So what you can do is you can say hello.

2:49 Oh, I keep doing that.

2:51 Hello, and you can say start from zero, and end at two.

2:54 Hello, and you can say start from zero, and end at two.

2:57 Not including two, but end at two.

3:01 So include zero, but don't include the two.

3:04 Which means that you really get the zeroth str um

3:07 zeroth index

3:09 and the first index.

3:11 Right, so whatever the letter is at the zeroth index,

3:13 and whatever the letter is at the first index.

3:16 So in this case we'll get an H E, okay.

3:21 How you can read this is just,

3:22 give me the first two letters, that's how I read it.

3:25 So you can just say give me the first two letters.

3:28 Now when you're starting off from zero,

3:30 by default index starts at zero.

3:33 So if you don't actually say this at all,

3:35 and you just remove the zero,

3:36 you're gonna get back H E, okay.

3:41 Everything that I'm showing you guys here,

3:44 play around with it, okay?

3:45 Don't just sit here and watch my videos.

3:48 I don't want you to be a passive learner,

3:49 please, please actively do this with me.

3:52 please, please actively do this with me.

3:55 Or pause my video and do this.

3:56 I want you to spend more time doing

3:58 and less time looking at it, okay.

4:00 Because it seems really simple when you're watching it,

4:03 but if you don't put it into action and do things

4:05 that make sense to you,

4:07 if you don't turn it into a game for yourself where you're

4:10 doing something, you know like

4:11 you making fun little stupid projects,

4:14 using what I'm showing you,

4:17 you're not gonna be able to remember it.

4:19 That's really what my problem with Codecademy is,

4:22 a lot of people go through Codecademy,

4:24 but the problem that ends up happening is that

4:27 they just go through it at a really fast pace

4:30 and they don't really have much

4:31 projects that they get to do there,

4:33 and not a lot of stuff that they get to do on their own,

4:36 so the most common complaint you hear from people

4:39 who take the Codecademy course will be like,

4:41 "It was great, I took the whole thing!"

4:42 But, yeah, right now, I can't write a single line of code,

4:46 okay, so it's not impressive the higher

4:49 you are in really abstract levels

4:51 introduction to classes,

4:52 "Oh yeah, I know all about function,

4:54 I'm in introduction to classes."

4:55 Write a function.

4:57 Write a function that takes in three inputs

4:58 and does dadada, print something out and sort in order.

5:02 "Pfft, I don't know how to do that, I'm totally lost."

5:05 Right.

5:06 Don't be one of those people,

5:07 make sure you build strong fundamentals,

5:09 and your coding level is functional at all times, right.

5:13 So even if I'm teaching you really basic stuff,

5:15 make sure you can do something with it.

5:17 That's the only way you'll get better

5:19 and make sure you have fun while doing it.

5:21 Anyway, let's get back to it.

5:22 So, hello, right.

5:26 Make up your own strings and break them up

5:28 and see what you can make up from what I have shown you here

5:31 and experiment, what if I change the end,

5:35 what if I change the stop part of it,

5:37 and what if I change the start part of it,

5:39 what if I don't put anything in the stop part, what happens?

5:41 So let's try that.

5:42 So hello and let's put in nothing, for both parts,

5:46 So hello and let's put in nothing, for both parts,

5:48 let's see what happens.

5:49 You just get the whole string, by default,

5:52 it starts from zero and by default

5:53 it ends at the last index.

5:57 Okay, so, it's the same thing as saying zero

6:01 to if you count it up, zero, one, two, three, four, right?

6:05 to if you count it up, zero, one, two, three, four, right?

6:06 O is four, so I'll say four here, that will not give me it

6:07 O is four, so I'll say four here, that will not give me it

6:10 I have to say five.

6:13 Right, because it will not include the four,

6:16 if I say four in will go up to but won't include the four.

6:19 For example,

6:21 see?

6:22 So we have to do five, okay?

6:26 So that helps us get to the end of the string.

6:30 Now what if I wanna get the last letter from hello?

6:33 Or anything, if I wanna get the last letter,

6:36 I can do something like this.

6:39 Negative.

6:41 Okay, I can also slice by a negative number.

6:45 So if I wanna get hell from hello,

6:47 I can do hello and I can say go from zero

6:50 I can do hello and I can say go from zero

6:55 and let's try see what happens if I put negative one here.

7:00 Right?

7:01 So another way I.

7:02 Basically, what I'm saying is,

7:04 start from the zeroth part go up to

7:09 the last part but not including the last part,

7:12 so that gave me hell.

7:14 Another way to write it is by putting a four here, okay.

7:17 Another way to write it is by putting a four here, okay.

7:21 Another way to write it is not having a zero here.

7:23 Another way to write this is not having a zero here.

7:26 That all gives you hell.

7:27 So you see, play around with all those.

7:29 I'm gonna now show you another thing

7:32 that you can slice with and that'll also blow your mind.

7:36 Slicing is very important, it's a very common procedure,

7:40 so it's pretty go to learn it because,

7:42 let's say you are trying to make an app

7:45 which goes on craigslist and pulls

7:47 a lot of data from craigslist,

7:49 so like pull up ads, so that ads, like

7:51 you might get the data back in a string form.

7:54 So you might get something like,

7:56 XBOX 360 pricing is,

8:02 it's price is $10 and

8:05 that's stupid, it's not $10, right,

8:07 you might get it for $150 nowadays,

8:11 2016 the value of it has significantly dropped,

8:15 and then let's say it says the condition type,

8:18 so the condition type is new, right.

8:22 So this is the

8:26 data that you'd get from craigslist.

8:28 Well, if you were writing up script or python code

8:31 Well, if you were writing up script or python code

8:34 that would pull that information

8:36 and then make sense out of it for you

8:39 and like write it to an actual excel file,

8:42 so like you want it to, you know, essentially do something

8:46 cool where it opens up a excel and writes to it

8:50 and you want it to like have,

8:53 you know, product,

8:55 price,

8:58 and condition, right,

9:00 and in product you'd want XBOX 360,

9:04 in price you'd want 150

9:07 and in condition you'd want new, right.

9:11 How would pull that data cleanly

9:13 so it doesn't put XBOX 360, 150, new all in one place?

9:17 so it doesn't put XBOX 360, 150, new all in one place?

9:21 Right?

9:21 So for that you need to be able to do string slicing, okay.

9:25 So for that you need to be able to do string slicing, okay.

9:28 So for instance, you might say,

9:31 console or product, right, or console product

9:35 is equal to, you know, find me the first pipe, right.

9:39 is equal to, you know, find me the first pipe, right.

9:42 So like let's say we have this guy here, there is a method

9:45 So like let's say we have this guy here, there is a method

9:48 you can do on data which is called index.

9:51 you can do on data which is called index.

9:54 So let's find the index of pipe.

10:00 It tells me that pipe is at index nine,

10:02 so zero, one, two, three, four,

10:06 five, six, seven, eight, nine.

10:10 Which means that if I index the string data

10:15 and I do nine, It'll give me back the pipe.

10:19 So what that tells me is that to get XBOX 360,

10:22 I need to go from the start of that string,

10:26 all the way up to the first pipe,

10:28 that should get me the product.

10:30 So I can say product is equal to data

10:33 from the start I don't need to say zero, right?

10:36 I can say from the start to

10:41 take the data dot index of the pipe.

10:48 Now if I show you product, boom.

10:51 Look at that, we got XBOX 360.

10:54 And so now I can write that product to the file,

10:57 teach you guys how to read and write to files.

10:59 Okay so then what tt will do is that it'll actually write

11:02 XBOX 360 in here for you, automagically.

11:06 Now, understand the power and implications,

11:09 "Well, why can't I just do that by hand?" Right?

11:11 That might be a question.

11:12 What if it was a hundred thousand products?

11:14 Can't do it by hand, good luck, right?

11:17 What if a million products that you were trying

11:19 to search from and find the best price

11:21 using your craigslist bot.

11:24 That's where programming comes in, okay?

11:26 It's very important to understand how programming in here

11:29 ties together and how it's more powerful

11:32 than you trying to do this on your own.

11:35 So that's really the power of string slicing, okay?

11:39 To break this line down for you a little bit more,

11:42 data, colon, that's just saying start from zero,

11:46 and then I'm saying data dot index of pipe,

11:49 what does that part evaluate to, right?

11:51 Dot index is a method that you can use on data, that's, okay

11:55 Dot index is a method that you can use on data, that's, okay

11:57 which just gives you something that's you're looking for,

12:00 you pass it into the function, right, that function

12:02 or that method index takes in one argument.

12:06 So what does this whole part evaluate to in our case?

12:09 This part evaluates to a nine.

12:12 Right, this whole part data do index, right?

12:16 Evaluates to nine, so if I do data zero through nine,

12:20 you can see that I just get XBOX 360, the same way.

12:23 Nine tells me up to but not including the pipe, okay.

12:26 Nine tells me up to but not including the pipe, okay.

12:29 So that's how we got the XBOX 360 part,

12:33 how would you get the 150?

12:35 You would kind of do the same way to get the price, okay.

12:39 You would kind of do the same way to get the price, okay.

12:40 But you would say instead of starting to look from here,

12:45 because then it'll find this pipe right here,

12:47 right, this one.

12:48 You wanna find this pipe now.

12:51 So you want to actually start your string search

12:55 from this location or this location that I'm highlighting.

12:59 And then you wanna search all the way up to this pipe

13:03 and stop there and get whatever

13:06 is in between these two pipes, okay?

13:09 So that's something I want you guys to try,

13:12 paste your code below for how you might get

13:15 the price and the condition, okay.

13:18 That would be a fun thing for you guys to do.

13:22 I'm gonna keep moving on

13:23 and talk a little bit more about string,

13:26 string slicing, cause there is still

13:28 a little bit more to it.

13:29 So

13:32 and again I want to keep practicing all this,

13:34 cause otherwise this is gonna overwhelm you,

13:37 all this knowledge.

13:40 So let's say that I have

13:44 I can do start, stop and here is another method

13:46 I can do start, stop and here is another method

13:48 to blow your mind, step.

13:50 So how many steps do wanna take when I'm reading something.

13:54 Okay.

13:55 So like let's say, I have this string,

13:59 "Hi how are you doing, it is very nice to meet you."

14:02 "Hi how are you doing, it is very nice to meet you."

14:07 I wanna make sure I'm consistent so not

14:10 double quote single quote and um

14:14 you know, let's just store that in some variable greeting.

14:17 Okay.

14:18 So if I say greeting so you can see the whole string,

14:22 so what I can do is take greeting, say start at zero,

14:28 stop at, I don't know, negative one,

14:31 so like all the way at the end,

14:33 and then I want you to.

14:37 Basically it'll go up to O, right?

14:40 Because it's up to like,

14:41 or sorry, it'll go up to the U part

14:44 but not this period right here.

14:47 Sorry.

14:48 I just, it won't let me highlight that period.

14:52 It won't go up to that period, okay.

14:54 It'll go up to U, because it's up to

14:56 but not including the period.

14:58 Sorry, I keep saying that a lot but I do know that

15:01 when you're starting to learn python or programming,

15:04 those things you'll forget a lot.

15:06 So I'm sorry if I'm reiterating

15:07 that fact over and over again.

15:09 Alright so we start from zero, we go up to the u, right?

15:11 Alright so we start from zero, we go up to the u, right?

15:14 We go from here all the way to here,

15:17 and then we wanna step, so instead of a,

15:23 for example, taking, I don't know,

15:26 reading every single one of these,

15:28 we can read every other letter.

15:30 So I can say instead of stepping by one which is default,

15:33 if I do one here you'll see,

15:36 this is pretty much the same string without the period.

15:39 And if I do nothing here, you'll see the same thing, right,

15:42 And if I do nothing here, you'll see the same thing, right,

15:44 cause that's a default.

15:46 And if I do step by two, this is basically saying

15:47 And if I do step by two, this is basically saying

15:50 give me every other letter.

15:54 Okay?

15:55 So think about maybe creating a game, gibberish game

15:59 that takes in a string as in a like it's a function

16:02 called gibberish, takes in a string and it just gibberi

16:05 called gibberish, takes in a string and it just gibberi

16:07 gibberish-izes it,

16:11 okay, it just like jumbles it up.

16:14 And if I do three here, you can see it stepping by three,

16:19 alright.

16:20 So pretty weird, but also cool at the same time,

16:23 So pretty weird, but also cool at the same time,

16:26 and

16:29 another thing that I wanna ask you guys as a practice to do

16:33 before I end this video is say I had the string hello,

16:40 I gave you the string, how would you reverse it?

16:45 Okay.

16:46 I want, if I gave you hello, I want back,

16:50 olleh.

16:52 Or if I gave you olleh,

16:57 you should give me back hello.

16:59 Okay.

17:01 So hopefully, that blew up your mind on string slicing,

17:04 So hopefully, that blew up your mind on string slicing,

17:06 I'll try to put some exercises on clever programmer dot com,

17:10 so if you haven't already go enroll in to the school

17:13 so if you haven't already go enroll in to the school

17:16 and there'll be exercises and extra resources

17:19 that you can use to get help.

17:21 Also there are others in the community who can help you.

17:24 Okay.

17:25 So good place to go for help,

17:27 but if you're watching on YouTube that's totally fine,

17:29 comment in the YouTube section below

17:31 and I will personally try to help you out,

17:34 other than that I'll see you guys in the next video.