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Welcome back, everyone, to the series of lectures on Python basics in this lecture, we're talking

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about strings.

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Strings in Python are used to hold text information and are indicated with the use of single or double

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quotes.

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We can also think of a string as a sequence of characters.

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And this is actually a super important idea the python, because this means there's actually an order

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to the string.

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So an example string would be something like ABCD PFG.

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So seven letters or seven characters.

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But what's really interesting here is Python understands that a is the first character of the string

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and pythons actually going to apply an index with each character.

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And it actually starts the index at zero.

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So, for example, the letter A is at index zero.

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The Letter B is an index one and so on.

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So you can actually use this indexing to grab particular elements or characters from that string.

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We're also going to be able to take what are known as slices of this string using bracket notation so

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we could grab multiple characters in a row if we wanted to grab ABCD, for instance, we could actually

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use bracket notation for that and we'll show you how to do that later on in the lecture.

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We should also note that strings are just Python objects or data structures and their methods, we can

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actually call directly from the string to transform it.

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For example, there's a method to uppercase every letter in this string, and we'll explore that as

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well.

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Now, the ideas of indexing, slicing and method calls are actually going to apply to many other objects

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and Python will be discovering.

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So I want you to keep that in mind as you learn them for strings.

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Well, are going to learn some things that are very specific towards strings, but then indexing slicing

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a method calls will be able to use that later on for other objects as well.

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OK, let's get started exploring strings in Python.

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I'm going to head over to our code editor.

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All right, so here I am inside our code editor.

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Let's go ahead and just quickly explain the use of single and double quotes within a Python string,

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so we can say Python string with single quotes.

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So I can say hello and single quotes like this, or I can also use double quotes to have that string

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there.

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Keep in mind that if I were to run this example python file right now, it's if I were to say Python

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example that Python go ahead and run that file.

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I don't see any output.

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That's because to actually see the output using the command line, I would need to actually print one

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of these strings.

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So now I can save that, run it.

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Now I see the output.

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OK.

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So single quotes or double quotes doesn't really matter.

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The one part where it actually may matter is if you actually want to essentially encapsulate something

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of a single quote or a double quote.

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So, for example, let's imagine the sentence I don't want to go.

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So this is a single quote, but it's just floating there.

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It's actually part of the word.

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What you can do with Python is you simply wrap it around the other type like this.

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I don't want to go.

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And let's actually cut that and put it inside our print function.

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And then I can run this in Python says, OK, I understand that this single floating single quote here

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is OK and it actually prints out.

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I don't want to go.

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So that's how you can deal with double quotes or single quotes that are inside something.

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You can just keep wrapping it around another set of quotes to actually understand or have Python understand,

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which is the quote and which is kind of the string quote.

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So what else can we do with strings?

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There's a bunch of different method calls you can use on a string to then actually change the string.

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You can also concatenate strings for this sort of thing.

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We're actually going to create a variable.

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So remember, I can assign variables by saying something like my variable name is equal to.

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And then let's go ahead and have it be a string such as.

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Hello, and let's go ahead and explore just a couple of methods on this.

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So I'm going to say Prince.

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My variable.

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And so when I read this, I should see.

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Hello.

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Now what are method calls on objects in Python?

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Method calls is when you have a variable like my variable here, and it's a specific data type within

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Python.

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You can call Dot.

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And then what's going to happen is there's a bunch of different methods you can actually call, which

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are going to affect the object.

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Later on, when we learn about object oriented programming, we're going to discover how to create our

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own methods.

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Now let me show you an example of one of these methods.

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There's a ton of them, and we won't use all of them.

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But I do want you to be aware of the fact that these methods exist on objects.

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They're essentially just transformations or augmentations you can perform on an object.

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So a really obvious one is something like upper.

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Now, often I see a student mistake is they just call the actual method, but they don't execute the

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method to execute the method.

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You have to actually call open and close parentheses on that method and add a little bit of spacing

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here.

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Just so it's clear what I'm doing.

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I'm calling my variable the method name, which sometimes you have to look up on the internet or a documentation

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to understand what this method does.

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And then you have open and close parentheses to actually execute or run that method.

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So upper, as the name implies, will actually uppercase every single letter here.

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So we're going to save that.

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Run that and now notice hello, isn't all uppercase.

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There's also things like capitalize, capitalize, this kind of similar just uppercase is the first

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one, so we save that change.

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Run that and then we see hello.

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Always remember that to actually execute methods, you have to actually call the parentheses if you

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just do this.

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And forget to do those princes and you run this, it doesn't actually give you an error, it just says,

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oh, there's a built in method that's going to capitalize a string object.

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And it's this memory location on your computer.

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Let me know when you want to execute it.

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So Python actually is pretty helpful in its kind of report to you.

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It just says, OK, that's a capitalization method call.

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It's on this object that lives at this part in your computer and memory.

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I should point out later on, we're going to learn about something called attributes, which are more

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characteristics of the actual object rather than transformations on the object.

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And those won't have open close princes on them.

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But for right now, you can kind of ignore those.

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This is all going to make a lot more sense when we actually create our own objects with object oriented

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programming.

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But I just want you to be aware of the fact that there's method calls you can call on a string.

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The last one, I want to show you something called split, which is actually going to create what's

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known as a list, which we're going to learn about next.

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But let me just make a little string here.

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I'm going to make a sentence that says something like, Hello, Mike, how is your dog?

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OK?

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So I can see I have a long string here and this is under my variable.

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And then I'm going to call Dot Split Open close parentheses with that split.

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This is by default, it's going to split this string into multiple components, depending on what you

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pass in for, what you should split on.

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So by default, it's going to split on blank spaces.

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So if I run this?

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It says, OK, here are all the single words inside that string, and it returns them as a list, so

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there's bracket notation here.

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This is actually a list in Python where it learn about it next.

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So just keep in mind that Split returns a list and you can split on whatever you want.

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So for example, if there was a comma here that said, Hello, Mike Comma, how is your dog?

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I could say split on the string comma note how I'm passing the string here with a comma.

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And this just tells Python, Go ahead.

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And instead of default, splitting on the white or essentially blank components here, the little spaces

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split only on commas.

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So use commas as your splitter.

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Now, if I save that change and I run this, I see.

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Hello, Mike, split into the first one and then how is your dog?

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The other thing I could do is maybe split on letters, so maybe I could split on the O's.

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Kind of a weird choice here, but it is possible so I can run this.

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And now I've split on the Oh, so every time there's an o, i go ahead and chop off the O and split

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so I can see how those chopped off mike space h o was shut off.

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Then W is y o shut off, etc. You kind of get the idea here.

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This will be really useful later on when we have to quickly maybe grab all the words in a sentence or

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something like that.

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So often you're just using the default, which is blank just to grab all the words in a sentence.

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OK, so we have the ability to run methods on our actual strings.

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The other thing I want to point out is we have the ability to index particular items from a string.

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So for example, let's imagine I wanted to grab h this very first h that is capitalized on the string.

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There's something called index notation and bracket notation that we can perform on objects to grab

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indexed items.

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The way this works is after the variable name you have open and close square brackets and then you're

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going to pass in the number of the index location of the letter you want.

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Indexing starts at zero, so this is zero one two three four, etc. So if I say for my variable index

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zero, that should return the very first letter in that string.

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So I run that and I see now, h.

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Let's go ahead and try to grab em this capital M.

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Well, how many index locations is that over?

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Remember?

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A string is a sequence of characters, and you should also note that spaces count as a character.

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So this is going to be zero one two three four five and then six.

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So if I now pass in six here, what's there we go.

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So five percent six for my index location.

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It grabs M.

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I should also note that indexing can technically go backwards as well.

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For example, if I wanted to grab that very last g instead of having to count all the way forward,

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I could starting at zero count backwards.

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So if h0, that means if I start going backwards in the string, this will be negative one.

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This g was going to be negative one.

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So we're going to see negative one here, save that change.

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Now I can see there is a dog.

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So again, indexing can go forward for positive numbers or backwards for negative numbers.

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Often we'll use negative one as a quick way to grab the last item in a sequence.

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Now that's indexing for a single item.

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There is also the ability to grab slices, as we mentioned.

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So let's imagine I want to grab the entire slice of hello.

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I want to grab that word using slicing.

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What's the actual syntax for that?

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Well, you say you're starting index points, colon and then the index you want to go up to, but not

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include.

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So it's inclusive of the starting point and it's exclusive of the end index point.

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So that means I'm going to say starting at zero go zero one two three four and then I'd have to go up

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to five because I'm grabbing everything up to, but not including that end index point.

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So I pass and five there save that change.

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Run that, and now I get.

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Hello.

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Let's imagine if I were to try to pass in for super common beginner mistake is they say, OK, let me

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just cut the letters.

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Zero one two three four.

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But what happens is the way the Python interprets this as you want everything up to, but not including

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four.

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So if you run that, you'd only get back.

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Oops.

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I forget to save that change.

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OK, so now if you run that, you only get back.

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Hell.

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OK.

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So again, this happens because it goes up to but not including that last index point.

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So this is slice notation.

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It's your starting point colon and then your endpoint that it goes up to, but not including the endpoint.

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The last thing I want to note here is the ability to actually use f string literals.

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So if string literals the way they work is, they're actually going to be able to insert different variables

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into a string.

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This is not super useful for us right now, but later on, when we learn about functions, it's going

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to be super useful to just insert strings.

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So, for example, we could be creating a website that actually takes in names and passwords, so I

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could say something like the first name.

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It was a.

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And the last name.

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His Porsche here.

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And then let's imagine I wanted to print out something like, Hello, first name, last name.

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So I say hello, and then I have two options here.

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I could manually type in Jose Porteus.

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I could say something like, Hello, Jose Portillo.

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But maybe this is part of a larger program where I want this to just work for anybody, not specifically

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for Jose Portillo, because once this changes to something like Mimi Portillo, then this is hardcoded

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in to be Jose.

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So what I want to figure out is how can I just by changing what's up here?

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Have the print statement reflect any changes in first name and last name?

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So if we run this right now, I get back.

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Hello, Jose Bautista.

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But I want to actually use these variable calls, so I only need to change what's up here once in case

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maybe I have something like prints.

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Last name is 40A, so I have to keep hard coding stuff in which is not what I want it to be flexible

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to these variable names.

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The way we do that is with f string literals.

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What you do is two steps one at the start of the string.

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Outside the quotes, you just put an F. There this f is just to tell Python, Hey, keep a lookout for

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variables that I'm going to put in curly braces inside the string.

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And as I mentioned then, the second step is wherever you have something you want to insert, you put

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in curly braces and then you're going to put in the actual variable name instead.

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So I can say hello variable first name space, and let's replace portela here with curly braces variable.

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Last thing, and then we're going to do the exact same thing here and to replace Tortilla here with

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variable last name.

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Save those changes.

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And now after you save those changes and run this, you'll see the exact same results.

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Hello, Joseph TRIA, last name is Tortilla, but now let's imagine up here, maybe in this form or

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something, I change this to.

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Mike Smith, save those changes.

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Now this is going to automatically update with just those variable names, so it's only dependent on

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the variable names, which you can then change up here.

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So now when you say and run, you see.

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Hello, Mike Smith, last name is Smith.

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Very useful, especially for inserting things that you don't know ahead of time.

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A lot of times you're not going to know ahead of time what the exact first name and last name is.

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Instead, it's going to be like user defined on the web page, so it's going to be really easy to then

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just insert it based off the variable names.

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OK, so that's it.

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The things we talked about here were just basics of strings.

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Different methods.

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You can call in strings indexing and slicing on strings and then print formatting on strings.

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I'll see you at the next lecture.