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  • Hey everyone, my name is YK. And i'm the founder of this YouTube channel CS

  • Dojo, and i'm also a former software developer at

  • Google and this is my, new

  • series python

  • Tutorial for absolute beginners and this is my video number 1: what are variables?

  • So this series is gonna be good for complete beginners, who have never done any programming before as

  • Well as someone who's done some programming before whether it's python or any other language but

  • Wants to learn more about python. So in this video i'm going to go through a number of different things

  • First of all what is python and what can

  • you, do with it and then i'm gonna explain how. To install python on your computer and then set up a development environment.

  • We're gonna use something called jupyter notebook throughout, this series and then i'm gonna explain how. To use the print function

  • And what are variables and how to use them and by the end of this video if you have two variables

  • Storing different things, you'll be able to swap the content within those two variables with

  • Each other, and i'm gonna put on

  • an outline of this video in the comment section below

  • So you, don't have to watch the whole thing if you, don't want to. Oh and before we get started if you?

  • Want to make sure that you don't, miss my future tutorial videos sign up to my, newsletter which is available in the description?

  • Below so just quickly, what is python and what can?

  • You, do with it it's one of the most popular programming languages out there and it's used at smaller companies as

  • well as larger companies including google and many

  • Universities use python as the introductory programming language in their computer science courses and one advantage of python

  • Is that it's fairly easy to learn because it has fairly simple syntax

  • It's used for many different applications

  • Including websites back-end code which is the code that runs on your server as

  • Opposed to the code that runs on your device whether it's a phone or a Laptop and it's

  • also popular for their analysis and scientific research purposes, okay?

  • So let's now go ahead and install python on your computer usually

  • When people develop a program using python or any other language for that matter they usually

  • Use something called ide which stands for integrated development environment. It's an environment that includes

  • Everything you need pretty much to develop a program. It has a nice text editor in which you can

  • Write your code and then the ability to run your program as, well as something called a debugger

  • Which allows you to quickly get rid of all the bugs in your program and if you, want to use an IDE to follow

  • My series i personally recommend park charms community edition so in this series instead of using a traditional

  • IDE i decided to use something called jupyter notebook

  • So jupyter notebook is an environment for writing and testing your program quickly and

  • It's actually, popular with the scientific community and for data analysis purposes but i've decided to use jupiter notebook throughout

  • This series because it's very simple and easy to install

  • Jupyter notebook through something called anaconda and it's fairly easy to use as

  • Well so here's the way, jupyter notebook, works there are two components to jupyter notebook

  • First of all when you launch jupyter notebook on your computer you might see a command line interface like this

  • This, represents the jupyter notebook server

  • You can, think of it sort of like the core of jupyter notebook and you don't have to worry that much about how

  • it works exactly

  • But just remember that if you close this window. Maybe accidentally jupyter notebook might stop working so just be careful about that

  • Now, when you launch jupyter on your computer you might?

  • also See a browser window or tab showing up whether it's Chrome, Firefox, Safari, or anything else and

  • It'll probably be at the url

  • Localhost call eight eight eight eight or something like that and it'll be connected to the jupyter notebook server

  • this

  • Browser window or tab is basically the user interface for jupyter notebook and you can write and execute your code

  • Here but it's actually executed on the jupyter notebook server, again. You don't have to worry that much about, how

  • It works exactly but this is just an overview

  • Now to install python and jupyter notebook we're, going to use something called anaconda

  • Anaconda is something called a package manager

  • which allows you to install many programs at once

  • This, particular package manager' anaconda is actually used for installing math and science libraries but

  • You, don't have to worry, about that the only thing you need to know

  • Is that when you install anaconda it comes with python and jupyter notebook so you

  • Don't have to install python or jupyter notebook separately on your computer

  • Let's now install python and jupyter through anaconda go to anaconda org, and then click download

  • anaconda and

  • Select whatever platform you're using whether it's windows mac or linux

  • I'm using mac here so i'm gonna click mac os here and there are two options here

  • Python, three-point-something or python 2 point something, make sure to use python 3 point something because we're

  • going to use python 3 instead of python 2 throughout

  • This, course so click download and then save this file wherever

  • You, want to save it and once this file is downloaded just open it and then click continue continue continue

  • Agree with everything and then select

  • Install for me only or install on a specific disk it doesn't matter which one you choose and then click install and

  • This, process will probably take a, while for you

  • Once this process is done you should see something like the installation, was completed successfully

  • Once you see that just click close and you're all set to launch jupyter you need to launch an application called

  • Anaconda navigator

  • Just launch that in the usual way you launch any other application, and then find jupyter notebook and click launch

  • Like i said before you see a browser tab or window. Opening up and it should be at the url

  • Localhost colon 8080 8th 8th or something like that

  • Ok, let's now. Create our first program

  • First go to whatever the folder you, want to create. Your first program, in i'm going to go to desktop

  • And once you click it you can see that my current location is desktop because it's at the top right here

  • Before you create. Your first program here i personally recommend that you create a

  • New folder so i just went to my desktop i clicked right click and then, new

  • Folder i'm gonna call this folder

  • python, tutorial 1 and

  • once you create that folder you should see in the jupyter notebook interface to click that and you see that the current location is

  • Python, tutorial one within desktop right here at the top to create a, new, file or a, new?

  • notebook, file as i say just click new at the top right hand corner and then click python 3

  • So a new notebook has been created, here change the name of this notebook from untitled to

  • Let's say, what are our?

  • variables click rename and

  • Once you, do that if you go back to desktop and the folder that

  • we just created python tutorial 1 you'll see a, new

  • File what our variables dot i pi and b and that i pi and b is just an extension for algebra notebook?

  • Now in jupyter notebook there's something called a

  • Cell each cell represents a set of code and the box you're looking at right now is one cell

  • So you can, type in any python code here for example print

  • Parentheses double quotes hello world and when you run, this? Cell

  • Using this button at the top it executes all the code within the. Cell, so let's run, this. Cell and

  • You, see that the string hello, world, is printed so this text hello?

  • World is something called a string it's usually enclosed by either double quotes or single

  • Quotes and it's basically just a set of characters so

  • Assuming that this is your first time coding in your life i'm going to explain

  • this, line a little bit more carefully so this says print whatever is in the parentheses these two parentheses and

  • that happens to be

  • Hello, world a string and when you run it again it's printed right below. This

  • Cell how the world and the important thing to note here

  • Is that if you

  • Don't type in the exact set of characters that you see on the screen it might

  • Not go right so for example if you forget to close the parentheses and run the

  • Cell you'll get an error and if you use

  • for example

  • Curly, brackets instead of regular

  • Parentheses you, also get an error and if you forget to close the

  • Quotation, marks it's the same thing so

  • Let's try, using this print function. A little bit more in

  • This, cell that you see right here in the green, box you can, type in print double quotes more string and

  • Actually instead of using double quotes you can, also use single quotes in python and then you can run this. Cell and

  • The string more string is printed

  • So you can, use single quotes and double quotes pretty much interchangeably in python and then you can

  • Also, print not just a string but, also a number so you can, say print parenthesis 3 and then when you run

  • The, cell the number 3 is printed and you could, also have multiple lines within the same cell as, well

  • So in this. Cell you can, write print

  • let's use double quotes here more string and

  • then print 3

  • So when you run, this. Cell these two lines are executed one by, one

  • so you see more string and

  • Three print it just one after another

  • So let's now dive into our main topic here namely, what are variables

  • Before i explain, what our variables exactly in python i'm going to show. You some sample code you can write a

  • Equals 1. And what this means?

  • Is that assign this value 1 this number to the variable named a

  • You can, think of it it sort of like the variable a

  • Containing the value 1 that's not 100%

  • Technically accurate, as i'll explain later but that's one way to think, about it so when you run this

  • Cell you, won't see anything printed this time but the variable a now

  • Contains the value 1 or a more technically accurate, way of thinking about it is that the bar a

  • Refers to the value one and you can. Check, what's inside the variable a

  • by

  • Printing the variable with print parentheses a and note here that there are no double quotes or single quotes around

  • This character. A, and that's because a is not a string it's a variable and when you run, the?

  • Cell you see the value a is referring to which is one and you can

  • Do the same thing with different variables so you

  • Can write b equals two so the convention here is you write b space and then

  • Equal space and to

  • This, line says, assign the value 2 to the variable b and when you run, the

  • cell again the variable b refers to the value 2 now so if you haven't for example c in this code and

  • If you, want to know, what's inside the variable or what the variable refers to you, can, write just like before print

  • Parentheses be no single quotes or double quotes

  • Run this. Cell with this button right here and then you'll see the value b is referring to

  • Just like before, we can, write multiple lines within a single cell right here

  • By, writing print parentheses a

  • print

  • Parentheses b and when you run, this, cell

  • You'll see one and two so one is what a is referring to and two is what b is referring to?

  • So a variable doesn't necessarily refer to a, number it could refer to a

  • String so if you write for example c equals either double quotes or single quotes hello

  • there

  • And when you run the, cell?

  • C now, we first see the value or the string hello there and when you print c?

  • You should see how low. They're printed

  • So i just ran this. Cell and the string hello, there has been printed, so let's now

  • Quickly, talk about

  • What variables are in python when you write a equals one in a different language for example c or c++

  • The correct, way to think, about it might be as a, box so you have a, box a

  • Containing the value one but in python this is not the accurate, way to think about it the more accurate way to think

  • About it is that a is more like a name tag and this can refer to any value you

  • Want and when you say a equals one you're saying a refers to the value one now. These two

  • Ways of thinking, about it they might not seem that different right now but it's

  • Going, to be more important later and in python you can create a, new variable, by writing as

  • We saw b equals 2 and this says the name b or the variable b now

  • We first see the value 2 and just like you saw

  • A variable can refer to a string as, well so if you write c

  • Equals hello, there you're, saying the variable c refers to the string. Hello

  • There once you master that basic concept you'll be able to move on to a slightly more advanced topic

  • Let's say you run, these lines of code and then you, want to run more code for example d equals 2

  • Then what happens is the variable d of course refers to the value to

  • Which the variable b also refers to

  • so it's totally possible for two or more variables in

  • Python to point to the same value in this case 2 and then it's

  • Also possible for you to reassign an existing variable to another value so if you

  • write b equals 1 after

  • executing this line of code b equals 2 after this line b refers to two of course but, after writing b equals 1

  • B refers to 1, which a, also refers to and you can

  • Even reassign an existing variable for example b which once referred to a number

  • One right here to something else for example a string so if you, write for example b equals double quotes ah

  • The string the variable b now refers to

  • The string ah

  • So let's see how, this actually works out in code

  • Okay, we're gonna continue on the code, we had earlier earlier, we had b equals

  • so if you print be

  • the variable

  • We get the value to and you can reassign

  • This variable to another value for example 1. By writing b equals 1 and then when you run the. Cell, and

  • print b again

  • you get

  • One printed the new value and what happens if we try to print a variable that doesn't exist yet

  • So if you try to print print

  • Parenthesis, a what happens let's run, this

  • Cell and see what happens it'll actually give you an error because he doesn't exist yet and the error says

  • Name error name e is not defined yet so that makes sense let's fix that. By writing e

  • equals this is a string and

  • This, way the value this is a string is assigned to the variable e and the variable e exists in the system

  • So if you print e with print parenthesis e and when you run this

  • Cell you, don't get the error anymore and let's address another question

  • You might have here is it possible for us to assign a variable

  • to

  • Another one the answer is yes so here if you write

  • Equals 1 a of course refers to 1. And then c equals hello, world c refers to

  • hello world

  • What happens if you write f equals a?

  • What happens then is this, means the variable f the name f refers to?

  • The value a is referring to so f refers to one now and so f?

  • doesn't refer to the variable a

  • Instead it refers to the value a is referring to and this is important for example when you do a

  • Equals two if you write that a now refers to

  • the value 2 instead of 1 but f

  • Stays at the value 1 and this might not be the case if f was referring to the variable a

  • Let's take a look at another example here if you write g iko see the variable g will refer to

  • Whatever the value c refers to which is how it world and then once you write

  • C equals, hello c will refer to the new value

  • Hello, right here

  • But the variable g will, stay at the value hello world

  • Okay, let's go back into the demo earlier in the demo, we had a