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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 is

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such a thing as a complex number in python.

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But we talked about the main ones that end and float 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 important

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term in Python.

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And as a matter of fact in all programming languages it's called variables.

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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 well this is very simple because all languages have variables but what

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are they.

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Exactly.

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Well variables store information that can be used in our programs.

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So we can hold perhaps user inputs like values maybe when you log into facebook you need to hold some

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information such as your profile picture or maybe your date of birth in a variable.

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Variables are ways for us to store information on our computer so let's have a look at this.

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If we remove this and let's say I'm creating a quiz program and this quiz program maybe measures your

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IQ let's say you just took the quiz and you found out that your IQ is 190 quite high.

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Good job.

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But we need to store that information somewhere where we can do that with variables so that in Python

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all we need to do is name it whatever you want in our case there'll be IQ and we're going to say IQ

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equals one 90 and this IQ here is a variable.

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It is something that I just completely made up.

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I can name it whatever I want.

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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 so we can pretend here that a user takes a

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quiz find out their IQ is one ninety we can store that information in this variable and later on when

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they come perhaps online or try to use the program again they don't have to take the quiz all over because

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well we store that information in IQ and remember what I said at the beginning programs are simply data

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that's being stored that's being changed that's being removed and that's all programs are and variables

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are important concepts in Python and all languages 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 to this variable so that when we request this variable later on

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in our program our computer knows how to look for this information it's going to say hey I know what

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IQ is I stored it somewhere a memory and it's going to go look for that and because it's being bound

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to a value it points to this value one ninety.

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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 we just want to be able

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to retrieve it.

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And then when we printed to do well get one item.

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Now we're gonna be using variables all over the course but on top of just naming variables however we

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want.

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There is some best practices around variables of how you should write good variables and as a matter

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of fact these are specific rules that the Python community as a whole has that you'll 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 snake case means it's

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all lowercase and then spaces while they don't exist we use underscores variables must start with a

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lowercase or an underscore variables can be anything with letters numbers and underscores.

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But remember they have to start with lowercase and underscore that means we can't start a variable with

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a number.

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There are also case sensitive.

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That means if I create a variable but let's say this snake case this variable has a capital E instead

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of a lower Casey there'll be a different 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 first.

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A variable has to be in the form of a snake case.

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That is if I want to call this user IQ I should technically have an underscore here instead of a space

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just to make sure that a programmer.

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Maybe I'm working on a team can read this variable so that's snakes.

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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 so now in order to access that

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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 course.

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

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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.

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So if I do user IQ here and I do.

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Capital letters 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 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.

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For example this print is a keyword.

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You can see it highlighted in blue so that if I create a variable saying print equals one 90 and then

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I do print print.

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Let's see what happens we get an error because I can't really assigned to this variable because print

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already means something.

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Now I know what you're wondering.

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What are these keywords 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 W3 schools you'll see that we have these keywords that each mean something

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in Python again.

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We'll go through these and we'll learn them throughout our course.

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And if you look it's not that intimidating.

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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 keyboard or an important word in in python.

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Well you see that it's highlighted in blue as soon as you create a variable that is unique.

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It's highlighted in white and this will be the case with whatever environment that you're typing code

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into as long as it's set up for python.

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Now beyond the python keywords there are different things like for example the I.A. for integer that

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we've learned so these.

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We're gonna get familiar with.

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So a good rule of thumb for variables is to make them really descriptive really say what your intention

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is and a good programmer is somebody that's able to name 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 90 and then I decide to perhaps have another variable call

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it user page and for some reason I want to assign user H to perhaps have IQ divided by 4.

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Is that going to work.

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It should.

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Right.

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I'm saying user age is going to equal forty seven point five I'm using IQ which is 190.

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Dividing it by four and then assigning it to user age.

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

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And once again I run this and it's printing the same thing so you can use variables to store that information

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and use it whenever you want.

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You can use it in operations you can use it to reassign it whatever your program needs.

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Now later on in the course we're going to learn about classes and classes actually have a different

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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 point

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1 4.

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We can have it all in capitals and that's going to tell other programmers that hey this is a constant.

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This number is not meant 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 it

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and reassigned it the value of zero.

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You can still do that but a good convention is that if you see this that means this number or this value

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should never be changed.

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Another type of variable that you're gonna see and this is something we'll see later on in the course

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are the.

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It doesn't look like I just did double on discourse here but it's two underscores and we call these

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Dunder.

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And as you can see here we have some Dunder variables that Python has now we'll learn more about these

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later on.

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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 high and assign it a

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value.

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I mean you still can.

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However this is generally not good practice.

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So you want to be careful with that but the one thing that I really want you to take away from this

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is that variables are really important concepts and programming naming variables is one of the most

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important skills we 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 gonna 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.

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The point of writing good code is that it's readable and understandable by other programmers by the

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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 1 2 3 and this simply is a way for us to rapidly assign values to variables multiple times.

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So for example if I do print a then print B then print C and I run this you see that I get 1 2 3.

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We assign value of 1 to a value of 2 to B and value 3 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 you in the next one.