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Hey, welcome to a new video on p.

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So far, we created two classes in our event Scraping app, an event class and an email class.

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Now we have two more functions which are floating around without a glass.

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So since we decided to make this an app, then it's a good idea to place all the functions inside classes.

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So what do you think should be the next class we should have here?

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So we have a store function and a read function.

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These two functions are working on a database, so this stores data in the database and this other function

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reads data from the database.

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So I think that these two should belong to a database class.

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So this is just the name I decided to give to this class.

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You can also call this database table or another name, so you should try to give your classes meaningful

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names.

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I'll just leave it database.

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Make some break lines in here.

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Add the self arguments to each of these.

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I'll cover today what self is.

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Now this class here is a bit more demanding that the other two classes.

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This class is also using this connection object in here.

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So first we establish a connection here and we store that connection in this variable, and then this

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class is using that variable or both.

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It's a better idea to have that.

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Expression inside the class.

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Since we are using classes now to organize our code, then what I'll do.

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I'll just cut this out from here.

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And where do we place that?

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So we have two methods the store methods and the read methods, and both methods use that connection

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variable.

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So one way is to have that expression in both methods here and here.

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Or both.

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This is not the recommended way to do this.

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We should place this expression somewhere where it is accessed by the two methods.

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So just once, instead of having repetitive codes like this, so I'll delete it from here and here and

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I'll add a special underscore underscore in it, underscore, underscore methods.

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So make sure that the method is named exactly like this underscore, underscore in it in lowercase letters,

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underscore, underscore.

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And this also has self argument as well.

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And the column and then the body of this method will be that expression connection is equal to you light

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that's connect, dot, dot, dot, db.

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Now this variable then should be accessed by the store and the reads functions.

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Currently, though, PA charm is giving us a clue that these methods do not have access yet to this

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connection variable.

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You see, it's underlined in red.

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It says unresolved reference connection.

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So basically this function, this method doesn't see that variable.

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To make that variable visible to these two methods.

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What we do is we add self dot in front.

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So now connection is a property of the self argument.

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Then in here we do the same self dot connection, self, dot connection.

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So now we point to that property to that variable, which is a property of self.

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And so self is like a special variable and all the methods have access to self, right?

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So we use self as the middleman to access the variables.

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So self dot connection, cell, dot connection.

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Same goes in here, self dot connection, and so on.

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And then when we call the the class here, down here we say if extracted and so on, we create a database

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instance using the database class, which is with a capital D, right.

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This class.

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And then in here we see a database with lowercase letters that reads and same here, database that store.

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And if you run the code now, it will work the same as it did before.

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Now, perhaps your data DB file has some data already, so make sure that you have an empty data DB

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file.

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Perhaps you need to redownload it from the lecture resources in the previous video so that you have

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a fresh empty database DB file and that will send you an email.

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If that's the case, when a tool is found, an event is found.

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But I guarantee you that this code works the same as it used to do when it had functions in here.

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Now, if you remember from the previous apps where we used to create PDF reports, we used to have.

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This line of code pdf is equal to f pdf where f pdf was a class.

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So a class which created PDF instances and this class got some arguments such as an orientation argument

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which was P or L or portrayed something like that.

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So this class used to get arguments of both our classes here database, event and email.

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They don't get any arguments, but we can also have them make it possible that they get arguments.

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So let's do that with this database class and then I'll explain you what self is and what in its method

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is.

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Exactly.

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So if you want this database class to get an arguments, you want to add that as a parameter of the

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init function or the init method.

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So the parameter could be, for example, database path.

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Right.

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And so this goes in here as well.

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Database path.

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Right.

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And then when you call the class here, let me fold this function.

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And this one in here.

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So I'm not deleting them.

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I'm just making them invisible for now.

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So the code is still there, right?

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I just want to do that.

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So you see the class and also these lines in here.

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So now in database, we say database path is equal to the value, which is the string data DB which

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points to this file.

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So now this class is getting an argument.

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So that's the argument and that's the value.

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So the way you give arguments to a class is by providing a parameter in the in its methods.

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So what is in it and what is self?

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Let me explain.

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These two very delicate concepts now in it is a special method, as I told you already.

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Why is it special?

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Well, it is special because this method is executed when you create an instance of the class.

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So specifically, when the interpreter runs this line here, this init method is called all the background.

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So perhaps if you had like a print function here.

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Hello.

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And you execute this code that hello will be printed out when the interpreter reaches this line here.

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Right.

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And you'll get hello in the command line.

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So I can also prove you that by opening the console here.

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Class food.

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Just a dummy class.

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Define an init method with self and not other arguments, but just print out hello like that.

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And then another method.

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Define do something with self.

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Print.

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I am the do method.

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Execute creates a new instance.

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Fu one.

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Equal to fu.

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When I execute that now hello will be printed out because this line here, as I mentioned, executes

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that method.

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But this other method is only executed when you point to foo one event to that method explicitly.

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So execute that and you'll get.

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I'm the do methods.

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Now what is self?

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Self is a special argument.

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So we have a special method and we have a special argument.

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Self.

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Self actually is the variable which holds the instance that is being created.

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So for example.

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In the food class here.

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This is an instance, right?

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And we can have multiple instances such as food.

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Two is equal to foo.

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Great.

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So we have a few one instance.

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We have a few.

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For instance, you'll see that these have different addresses in memory.

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So you see that this has this address.

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This has another address.

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These are just random IDs that are assigned by Python.

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So but I'm trying to tell you that these are like different objects, different instances.

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And so self is like the variable which holds the instance inside the class.

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And so when you say self, that connection, you are pointing to the connection of that particular instance.

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Let me try to explain it better.

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I know this is confusing, so let's create another class.

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I'll use an arrow key to call this previously executed statements.

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So the class.

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But this time I'll go up here and I'll add a new argument.

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Let's say X, right?

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And then I'll say self that x is equal to x.

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Execute.

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Now FU three is equal to FU with X being one and FU four is equal to FU again with x being two.

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Know fu three dot x gives you one while fu for that ex gives you two.

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So that proves my point that foo three and foo four are different instances.

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So you can try to imagine this like being the self argument.

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But outside the class it's not called self.

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It's called the variable name which holds that instance.

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But inside the class it's self.

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So basically foo three dot x is self, dot x.

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So when the user gave the x value to x here, that value went in here first.

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So x is equal to one, right?

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And then self does x is equal to one.

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So this x here is that x, right.

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So one is assigned to self that x.

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So that's the property of self and that's just an argument.

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It's a bit confusing, but that's why we have applications and you'll see how you'll use self in different

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scenarios and that will become second nature to you.

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But through now.

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This is what you should remember.

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So let's make a revision of what we did in this video.

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So you learn the init method which is executed when you instantiate the class, when you create an instance

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of the class.

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So init is executed in here, then we have self, which is a variable inside that class and it holds

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the instance that the user is creating.

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And then we have other methods such as tool and reads.

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And then we have properties such as connection here or this X here, right?

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That's a property, that's a method and that's what you should remember for now.

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So these are concepts that we will revise again using different examples.

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So don't worry if you don't get things right away and I'll talk to you in the next videos.