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0:00
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
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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
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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?
1:21
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
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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
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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
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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
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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?
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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
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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
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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
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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
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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
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Just launch that in the usual way you launch any other application, and then find jupyter notebook and click launch
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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
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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
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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
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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
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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
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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
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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
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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
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So in this. Cell you can, write print
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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Let's rename this notebook. By clicking untitled and by changing it to
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swapping two variables and
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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
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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
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Second string, so that's v1 referring to this string and v2 referring to this string, we can just write
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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
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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
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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
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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
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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
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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
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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?
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