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Welcome back.

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So we've just learned about the first two, well, kind of three, because we also mentioned that there

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is such a thing as a complex number in Python, but we talked about the main ones that aren't and float

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and there are still a few data types remaining.

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But before we get to these, we are missing an important concept, and this is going to be our first

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important term in Python and as a matter of fact, in all programming languages.

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It's called variables, yep, that's a term.

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Now, if this is your first time learning a programming language, you might not know what this means

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if this isn't your first time.

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Well, this is very simple because all languages have variables.

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But what are they exactly?

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Well, variables store information that can be used in our programs so we can hold perhaps user inputs

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like values.

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Maybe when you log into Facebook, you need to hold some information such as your profile picture or

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maybe your date of birth in a variable.

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Variables are ways for us to store information on our computer.

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So let's have a look at this, if we remove this and let's say I'm creating a quiz program.

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And this quiz program maybe measures your IQ and let's say you just took the quiz and you found out

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that your IQ is 190 quite high.

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Good job, but we need to store that information somewhere.

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What we can do that with variables so that in Python, all we need to do is name it, whatever you want.

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In our case, it will be IQ and we're going to say IQ equals one ninety.

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And this IQ here is a variable, it is something that I just completely made up, I could name it whatever

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I want, that's a variable, too.

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The idea is that once we assign to a variable, that is we're saying one ninety is going to be assigned

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to IQ.

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I can now use it in my program whenever I want.

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For example, I can later on print or make sure it's not cap.

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Let's do print IQ.

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And if I do that and click run, you see that I can use IQ.

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So we can pretend here that a user takes a quiz, finds out their IQ is one night, we can store that

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information in this variable and later on when they come perhaps online or try to use the program again,

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they don't have to take the quiz all over because, well, we store that information in IQ.

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And remember what I said at the beginning, programs are simply data that's being stored, that's being

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changed, that's being removed, and that's all programs are and variables are important concepts in

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Python and all languages.

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Now, variables can also sometimes be called names.

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So this could be a name, for example, in assigning a value is also known as binding.

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That is where binding the value one Nidhi to this variable so that when we request this variable later

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on in our program, our computer knows how to look for this information.

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It's going to say, hey, I know what IQ is.

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I stored it somewhere, a memory, and it's going to go look for that.

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And because it's being bound to a value, it points to this value one.

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And remember, this number in memory gets stored as a binary representation in zeros and ones.

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Right.

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But it doesn't matter to us because however our machine stores it, we don't care.

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We just want to be able to retrieve it.

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And then when we print it to do well, get one 180 now we're going to be using variables all over the

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course.

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But on top of just naming variables however we want, there is some best practices around variables

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of how you should write good variables.

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And as a matter of fact, these are specific rules that the Python community as a whole has that you'll

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just have to remember.

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So let's have a look at this variables.

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And remember, this is the symbol for best practices are what we call snake case.

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Snake gas means it's all lower case and then spaces, while they don't exist, we use underscores variables

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must start with a lower case or an underscore.

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Variables can be anything with letters, numbers and underscores.

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But remember, they have to start with lower case and underscore.

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That means we can start a variable with a number there.

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Also case sensitive.

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That means if I create a variable.

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But let's say this nakase this variable has a capital E instead of a lower Kacie, there'll be a different

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variable.

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And then finally, you can't overwrite keywords.

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Let's go through these with some examples.

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First, a variable has to be in the form of a snake case, that is, if I want to call this user IQ,

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I should technically have an underscore here instead of a space just to make sure that a programmer,

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maybe I'm working on a team can read this variable.

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So that's snake case, you also have to start your variables with either a letter or an underscore.

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So I can technically do this and I click run.

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Well, that's going to give me an error because I've changed a variable.

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So now in order to access that variable, you have to go like this.

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Now, underscore in python signifies a private variable, something that will go over later on in the

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course.

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But usually you're starting your variables with a letter and afterwards, yeah, you can add numbers

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if you want in here.

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That's no problem.

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This is still going to work.

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This is a valid variable.

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Finally, a variable is case sensitive, so if I do user IQ here and I do capital letters.

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I can't access this.

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Like this, because while it doesn't exist, again, it's case sensitive, we have to make sure that

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we match.

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And finally, we don't want to overwrite key words.

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What does that mean?

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Key words in Python.

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Well, they already mean something in Python, for example, this print is a key word.

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You can see it highlighted in blue so that if I create a variable saying print equals one ninety and

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then I do print.

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Print.

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Hmm.

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Let's see what happens.

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We get an error because I can't really assign to this variable, because print already mean something.

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Now, I know what you're wondering, what are these key words in Python?

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That's a simple Google search away and we'll learn these throughout our course.

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If we go to python keywords by three schools, you'll see that we have these key words that each mean

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something in Python.

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Again, we'll go through these and we'll learn them throughout our course, and if you look, it's not

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that intimidating, there's not that many.

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So as we practice, you'll start to get familiar with them.

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But the easiest way to tell whether it's keyboarder or an important word in in Python.

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Well, you see that it's highlighted in blue.

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As soon as you create a variable that is unique, it's highlighted in white.

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And this will be the case with whatever environment that you're typing code into, as long as it's set

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up for Python.

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Now, beyond the python key words, there are different things like, for example, the ante for integer

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that we've learned.

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So, Lisa, we're going to get familiar with so a good rule of thumb for variables is to make them really

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descriptive, really say what your intention is, and a good programmer is somebody that's able to name

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things really well with their variables.

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So if a new developer comes and looks at your code, it's easily understood.

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Finally, variables can also be reassigned.

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For example, let's say we have IQ here of one 190 and then I decide to perhaps have another variable,

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call it user.

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And for some reason, I want to assign user age to perhaps have an IQ divided by four.

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Is that going to work?

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It should write, I'm saying user age is going to equal forty seven point five, I'm using IQ, which

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is 190, dividing it by four and assigning it to user age.

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I can maybe assign this to another variable called user age or called a and once again.

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Run this and it's printing the same thing so you can use variables to store that information and use

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it whenever you want.

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You can use it in operations, you can use it to reassign it.

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Whatever your program needs now, later on in the course, we're going to learn about classes and classes

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actually have a different convention than this, but we'll get to that later on.

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For now, though, I want to mention two small gotchas with variables that you should be careful with.

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For example, there's an idea of constants and constants are those things that never change in a program.

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For example, if we wanted to create a constant such as the value of PI, let's say for now it's three

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point one for we can have it all in capitals.

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And that's going to tell other programmers that, hey, this is a constant this number is not meant

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to change.

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I mean, we could change it if we want.

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There you go.

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I just made PI equal to zero, so it was stored as three point one for a memory, but then we overrode

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it and reassigned it.

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The value of zero.

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You can still do that.

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But a good convention is that if you see this, that means this number or this value should never be

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changed.

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Another type of variable that you're going to see, and this is something we'll see later on in the

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course are the.

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It doesn't look like I just did double underscores here, but it's two underscores.

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And we call these Dundar.

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And as you can see here, we have some Dundar variables that Python has.

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Now, we'll learn more about these later on, but the idea here is that these are meant to be left alone.

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You should not touch them.

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You shouldn't create a variable with two underscores like this and call it high.

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And assign a value.

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I mean, you still can, however, this is generally not good practice, so you want to be careful with

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that.

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But the one thing that I really want you to take away from this is that variables are really important.

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Concepts in programming.

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Naming variables is one of the most important skills you have as a programmer.

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I know it sounds silly, but there's so many times that I read code that is so hard to understand simply

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because a programmer is not descriptive enough.

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So throughout the course we're going to learn how to name things well so that our code reads like English.

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And that's the whole point of writing a code, the point of writing a code is that it's readable and

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understandable by other programmers, by the way, to finish off.

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I just want to show you one quick trick.

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There's also a way that you might see in some code bases that uses something like this.

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He calls one, two, three.

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And this simply is a way for us to rapidly assign values to variables multiple times, so, for example,

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if I do print A, then print B, then print C and I run this.

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You see that I get one, two, three, we assign value of one to a value of two to B and value of three

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to C.

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Just a quick shorthand way that you might encounter.

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All right, let's take a break and I'll see in the next one.