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Hi.

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Welcome back.

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I'm very excited that today you will learn object oriented programming.

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So let's begin to be able to follow this video.

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You need to download the three files in the lecture resources.

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So that is the data db, file, extract, y, M, ML and Main P.

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These are the files of the previous app, the Scraping Tools SQL App.

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So please create a new patch on project and copy those three files into that project just like I've

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done here.

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Now what we will do in order for you to understand object oriented programming is we will rewrite this

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app by using the object oriented programming paradigm this time, so using classes instead of functions.

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But just before we do that, I want to refresh your memory.

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I want to quickly explain what this app does.

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So these are the import statements and this shrink here is actually not needed.

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We just left it there temporarily, but then we forgot to delete it.

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So we don't need those two strings.

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You can delete them.

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And so here we establish a connection to the database data.

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DB Which should be located in your project directory, this one in here.

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This database file that I gave you has an event table which is currently empty.

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Then we have this scrape function.

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What this does is it visits this URL in here which points to this website.

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Right.

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And then this function.

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Gets the source code of that page, which corresponds to.

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This HTML code here.

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And then this other function in here gets that source code that this function returns and it extracts

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only this part, which sometimes is an event, a musical event of a band.

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It contains the city and the date of the event.

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And sometimes this changes.

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So if I refresh the page, sometimes we have no upcoming tools.

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Sometimes we might have another event playing here, and other times it could be the same event and

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so on.

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This function returns only that value, whatever it is, no upcoming tools, all the events.

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Right.

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So then this other function here sends an email.

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That's what the responsibility of this function is.

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It sends an email to that receiver email address.

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That's it.

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Then we have this other function store, this other function.

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Gets the event this value and it stores it in the database using this SQL query here in that data DB

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database.

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And this other function reads the existing data of that data DB database.

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And it returns those data.

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So it returns the rows, which is like a tuple containing different lists, different values, depending

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on how many values we have in the DB file.

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And this part here is where we call all this functions, which is this here.

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So we run a loop and then in every iteration we get first the source code of the page using the script

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function, this script function in here.

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And then we extract the value, which could be no upcoming tools or something else.

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We store that value in here and then we say if the value is different than than no upcoming tools.

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So if there is an event on the page, then we read the existing events from the database using the read

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function.

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So we return the existing events.

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We see if we have stalled at events already.

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If not, if there are no such events, then we store the event because the event doesn't exist in the

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database.

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So we store it and then we send an email to ourselves, letting ourselves know that there was a new

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event in the website, a new event which was not in the database, and so we should know about that.

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That's what this app does.

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No.

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We can rewrite this using classes.

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So let's do that.

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Let's install these packages first requests and select your lib.

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So we get rid of these underlines.

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And let me create the first class to do that.

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Please select these two functions.

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Scrape and extract and then press tab.

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Tab will indent those functions with four space characters and then create some space in here and on

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top, say class, tool or event, whatever you prefer.

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I'll just leave it event.

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And then in the function parameters you need to add self as the first parameter comma followed by the

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other parameter that the function already has.

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Same for this self and that.

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And have another brake line here because that's what it is recommended to have.

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And here you need one brake line.

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So this is not mandatory, but it's a good practice.

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So to break lines after the class definition to Berkley's before the class definition.

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So this here is a class definition or just class for short, and a class is made of functions.

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So this class here has two functions scrape and extract, but we don't use the word function anymore

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when we are working with classes.

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Now these two are called methods actually.

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So we have the extract methods and we have the scrape method.

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So these two methods belong to the event class.

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Later, I'll explain you what self is, but for now you can just ignore that and you'll understand it

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later what it is.

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Now, you would ask, Well, why would we use a class?

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Why not just leaving those functions as they were?

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Well, but as you can see, this gives us a better way to organize the code because we have so many

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functions here.

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So it makes sense that you categorize them into classes.

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So these two functions, basically they belong to the event class because they scrape the page that

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contains the event and then they instruct the event.

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So it's a good idea to place them inside a class called event.

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Now you can also name this class like that.

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It is possible, but it is not recommended.

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And also partition will tell us that class names should be camel case, which means starting with a

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calculator.

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And if the word has two parts like.

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It could be a good event.

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Then you use a capital letter in here, no spaces or underscores, but a capital letter for the second

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name.

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And here we only have one.

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So let's just keep it event.

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Right.

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So that's the class definition of both.

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Now we need to change the way these methods are called here.

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So currently we still have them behave like functions.

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And PA charm is telling us that oh, there is no function with the name scrape, which is true because

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scrape is not a function anymore in the global namespace.

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Now this function is methods and it belongs to that event class.

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So before you call that method, you first should create an event instance by calling that class.

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So the way you call that class is like this event, the name of the class followed by parentheses.

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So this is similar to how you call a function later.

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You will also see that classes can also get arguments like functions do.

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But for now, let's just focus on calling a class without arguments and then event will be the variable

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where the instance of the class will be stored.

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Right?

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So you can have many instances now like event one event event to.

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Event.

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And when you learn about arguments, you'll see that these different events can take different values

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for the arguments and so on.

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So let's just ignore multiple instances for now.

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For now, you should know that this creates an instance and without parentheses is just a class.

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So once you create an instance, an event instance, then in here you should point to that event instance.

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So you see events with lowercase letters.

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So we point to the instance that scrape.

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Same goes for extract.

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Extract is also a method of the event instance.

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So events that extract event that scrape.

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And if we run this code now, it will work exactly the same as it used to do when we had functions in

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here.

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So the functionality of the code doesn't change when you use object oriented programming.

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What changes is the structure of the program.

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So object oriented programming is good for you as a programmer or for your collaborators, other programmers

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who are collaborating on the same app because it gives you a well structured app which is easier to

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extend later and it's easier to modify.

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Now, Python might give you some advice here.

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Maybe this method is static, it says, but feel free to ignore that.

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We'll talk about static methods later.

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No.

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We can do the same with the SANS email function.

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So the idea is that when you use object oriented programming, every function is categorized in objects

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or classes.

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So we use the term class and object interchangeably sometimes.

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That's why it's called object oriented programming.

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So your code is built around objects.

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The first object we created was event.

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So that's the object.

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And then this is the object instance here.

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So it's an instance of that object when we create later a ticket class for a hotel reservation app or

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an airplane reservation app, then ticket will be one class, but users will create multiple ticket

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instances, right?

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A user will create their own ticket using that class, that blueprint, and other user will create another

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ticket and so on.

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So that is one object, and then the other object would be class email and this class would have that

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method.

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So select that press tab to indent it, make a break line here to have to break lines here and to break

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lines in here.

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And so this class now has a sent email methods which perhaps we can rename this into send.

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Why did I rename it?

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Well, because let me show you why.

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So we go here then, and we don't call the send email function, but we say email.

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We create an instance of email class, which we just created.

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And then in here we say email dot, just send.

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So it makes more sense to say email that send, then email that.

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Send email.

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Right.

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So by using classes now you have more freedom to use shorter names.

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So now you know that this send method belongs to the email class, so things are more categorized.

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Yes, we do have some longer code because we added a class here, right this line.

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And then we we add the instantiation part of the class here and here as well as well.

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But longer code doesn't necessarily mean worse code.

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The code should be readable and it should be extensible.

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That is what makes good code.

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And that's about this video in the next video.

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We will work on creating a class for these two.

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The process here will be a bit more advanced, and that is where you learn about the init method, which

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is a special method and also about self.

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Which should also be here, by the way.

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So self should be in every method of the class most of the times, because sometimes in special cases

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you might omit self.

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But that's a special case which we will cover later on.

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So that's.

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About classes in a superficial level, but we have a lot more to cover.

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But for now it's enough to remember the syntax of classes.

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And let's move on to the next video.

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I'll see the.