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Python Tutorial for Absolute Beginners #1 - What Are Variables?

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

equals one and

Then c equals hello there

So once we print a and c. With print parenthesis a, and print parenthesis c

We should see one for a and hello there for see what happens if we write f?

equals a

F should now refer to whatever a refers to

So if we print f?

We should see the number one printed and?

What happens if we assign a to two?

then

The value of a should, now be two and then the value of f should, stay as i said earlier

at one

Okay, now i'm gonna give you a quick practice problem to work on in order to solidify your understanding of variables and to do that

Go, back to the previous tab of jupyter notebook the navigation

Menu and if you already, close the tab

Just open localhost colon 8080 eight eight or just relaunched

jupyter notebook

And then go back to the same folder as before we had python tutorial one click new in the top right corner click

python 3, again and

Let's rename this notebook. By clicking untitled and by changing it to

swapping two variables and

Here's the problem you're given two variables let's say

V1 equals first string in double quotes and v2

Equals second string, again in double quotes how

Can you, swap the values within, these two variables with

Each other the easiest way to solve this problem is just to write v1 equals second string and

Then b2 equals

First string, but this might not be the best solution

Because if you had a much longer string it would be kind of cumbersome to repeat these strings and

Then if one of the strings changes so if first string becomes first two strings

That you need to rewrite your code right here to

Match that to write first two strings again

So ideally you, want to be able to solve this problem without repeating the strings think

About it for a second and then i'm gonna show

You, what a good solution might look, like, when you see this problem you might say, well it's actually pretty simple

Once we have b1 equal to first string and v2 equal to

Second string, so that's v1 referring to this string and v2 referring to this string, we can just write

V1 equals v2 and then v2 equals v1 and we're done but actually this solution is wrong

Because when we execute this line v1 equals v2

V1 now refers to whatever v2 refers to of course, which is second string and then when?

We write v2 equals v1?

V2 will now refer to what v1 refers to now

Which is second string so at the end of these lines of code?

Will have v1 and v2 both refer to the second string which is not what, we want?

Let's now see what a? Good solution might look, like

I'm going to give you a few different options here the first option is to use two temporary variables we're

Gonna call them temp 1 and temp

2 temp 1 will be equal to

What v1 refers to so that's first string and then temp, 2 will be equal to what v2 refers to

Which is of course second string and then we'll just need to swap them together

So v1 will be equal to temp 2, which refers to second string so v1 will now refer to

Second string

After this line right here and then v2 will be equal to temp 1 which of course first string

So v2 will refer to

First string, after these lines so this is one potential solution but actually

We don't have to use two temporary variables

Okay, here's a solution that only uses one temporary variable instead of two the first thing we're gonna do is we're gonna set a

New, temporary variable called temp - what v1 refers to

so temp

will be this string right here and

After that we'll set v1 to v2

So v1 will no longer refer to first string. And then it will refer to second string instead and at

This point note that the first string this string is not lost yet because

We have a variable pointing to that value so after that all you need to do is

Refer v2 back to whatever temp refers to which, is first string so v2

Will refer to first string, after these lines of code and the v1 will refer to second string and

this, little pattern of using a single variable to switch the values of two variables is

Actually really important to know because it's a very common pattern to use for any programmer

Okay, let's now test that pattern with our python code so in the second sale we're going to write our solution

We're gonna create a, new variable called temp, which refers to whatever v1 refers to which

Is first string, and then we'll set v1 to be v2

So v1 at this point is second string and then we'll set v2 to whatever

Temporary first - which is first string so at this point

Once we print v1, we should be able to print second string?

We do and then if we print v2 which would see first string and?

We do okay, to download the files i created, throughout, this video just go to cs. Dojo io

Python 1 or if you just, want to subscribe to my, newsletter so that you don't

Miss my future tutorial videos just go to cs. Dojo dot io

News and as always let, me know in comment below, when you thought of this video i'm? Yk, from cs

Dojo, and i'll see you in the next video?