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Now that we've seen how we can create a new class.

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Even if it's a class with nothing inside.

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And we've seen how we can create a new object from that class

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by using the same code that we used in yesterday's lessons.

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The next question is: "Well, how do we create an attribute for that class?". Well,

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one of the easiest ways of doing this is simply tapping into your object and

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then adding an attribute.

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So we could say user_1.id = 

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"001".

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And we could add as many attributes as we want just by using this method of

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using the dot notation after the name of the object,

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and then just adding any piece of data we want. So now,

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if I go ahead and print user_1.username,

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you'll see that this attribute now exists in this object

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[Inaudible]

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And you can see the value that's held in that attribute being printed in the

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console. So just a quick reminder,

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an attribute is a variable that's associated with an object.

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So it's almost as if we just created a new variable, but in this case,

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we've attached it to an object. But here's a question though,

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if we had lots and lots of attributes like this,

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and every single time we create a new user,

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let's say we created user_2 and we had to do the same thing,

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create it from the class and then say,

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user_2.id = "002",

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and user_2.username

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= "jack". And this is one,

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a little bit prone to error because it's perfectly valid for me to make a typo

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or change the name of an attribute where I end up with something like this.

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So is there a way of making this simpler?

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How can I specify all these starting pieces of information

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when I create my object from the class? Now,

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in order to do this, we have to understand something called a constructor,

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which is a part of the blueprint that allows us to specify what should happen

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when our object is being constructed.

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And this is also known in programming as initializing

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an object. When the object is being initialized,

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we can set variables or counters to they're starting values. In Python,

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the way that we would create the constructor is by using a special function,

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which is the init function.

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And you can tell it's special because it isn't just the Def keyword

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and then the name of the function. It's got two underscores

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either side of the name.

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And this means that it's a method that the Python interpreter knows about and

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knows that it has a special function. Now,

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what is the special function? Well, it's normally used to initialize the attributes.

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So if inside our class

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we add this init function and you can see as soon as I write def and then 

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init, I've really got autofill helping me so I can just hit enter

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once it's selected. Now,

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inside this init function is where we initialize or create the starting

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values for our attributes. Now,

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the important thing to remember is that the init function is going to be called

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every time you create a new object from this class.

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For example, if I print,

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then every time that this construction happens

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when we create a new user,

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then this print statement is going to be triggered.

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So you can see here, this print statement gets triggered

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and then we print the user_1's username, and then we've got 

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another user being created. Just as a quick reminder,

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the attributes are the things that the object will have.

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And they are basically just variables that are associated with the final

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object. So for example, if you're constructing a car bject,

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then one of those attributes could be the number of seats it has and

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normally that's equal to five.

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So how do we set these attributes in the constructor? Well,

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this is what the code would look like.

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We have our init function and inside the init function

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in addition to this thing called self

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which is the actual object that's being created or being initialized,

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in addition, you can add as many parameters as you wish.

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And that parameter is going to be passed in when an object gets constructed from

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this class. And once you receive that data,

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then you can use it to set the object's attributes.

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This is what it would look like when we actually call our constructor.

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We know that we can create an object by calling the name of the class and then

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adding the parentheses. But if inside our init function

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we have some additional parameters,

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then we can also pass in data to those parameters

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which will be used to set the attributes for that object.

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So in this case, once this line of code has completed,

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then my_car.seats is going to be equal to five.

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And this is exactly the same as if we created our

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my_car object first and then we said my_car.seats = 5.

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It's completely the same.

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But it does make it a lot quicker when you're creating a lot of objects that

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need all the same attributes. Let's see how we would do it here.

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We've got our init function already declared.

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So if we wanted to pass over a user ID

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when we construct our objects, we can add that as a parameter

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and then inside the init we can say self.id,

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so self.id is going to be the attribute that's associated with this class

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and we can set it equal to the user_id that's passed in when any user gets

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constructed. So now when we create our user,

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instead of creating these attributes later on, at the time of construction

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you can already see that we can add a user ID.

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So let's give it the same ID.

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And now let's add another attribute.

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So we're going to pass in the username and I'm going to set the attribute

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self.username equal the username that's past it.

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Notice how in this case I've named my parameter user_id

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and that value is going to become the self.id attribute.

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So notice how these two actually have different names.

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You can name either of these anything you want.

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It's normally convention that you will see the name of the parameter be equal to

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the name of the attribute, but you don't always have to stick to these rules.

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Now let's go back to our constructor whereas previously it was empty,

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now we have our user ID being passed in and I can now pass in the second

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attribute, which is the username. So my username was going to be Angela.

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And now we've created a new user,

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which is user_1 from this user class

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and we're initializing it with these starting values where the first value is

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going to become the user ID which is going to be the self.id,

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and the second value is going to become the self.username. So now,

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if I wanted to print the user_1's username,

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then I can simply write

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user_1.username exactly the same way as before,

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or if I wanted the ID, it would be user_1.id.

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So now let's comment out the rest of the code and hit run,

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and you can see we've got the user ID being printed here. Now,

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remember that when you add parameters to the constructor

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which is the init function,

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you're now saying that whenever a new object is being constructed from this

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class, it must provide these two pieces of data.

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If we uncomment this and you try to run it, you'll see you get an error.

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And it says that on line 12,

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this user is being created from the user class.

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But according to the init, we're actually missing two required arguments;

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user ID and username.

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So now when we create any object from this class,

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we have to provide the user ID and the username.

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But this is now much more convenient, right?

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While we previously needed three lines of code, we now only have one.

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Now sometimes when we're creating our attributes,

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we might want a default value to start with.

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And if at some later point in our program we want to modify it,

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then we'll do it at that point.

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But it doesn't make sense for all attributes to be initialized when we actually

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create our object. So if, for example, in our case,

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let's say that we were coding up the Instagram app, right? Well,

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each of the Instagram users, they would have an ID,

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they would have a username and they would probably have a follower count.

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So they might have something like self.followers.

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This is always going to start out as zero, right? You start a new account,

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you're going to have zero followers. You might get some followers later on,

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you might not.

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But it doesn't make sense for followers to be something that we have to provide

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whenever we construct a new object.

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It seems very wasteful to have to always write zero

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when you construct any object from this class. So in Python,

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we can also provide a default value just as I've done here.

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Instead of setting it equal to one of the parameters that's being passed in when

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this class is being initialized, instead I'm just setting it to a value,

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which is zero. Let's get rid of that from the initializer

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because we now have a default value of zero.

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And if I go ahead and print my, let's say,

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user_1.followers attribute, and I hit run,

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then you can see it's zero because all objects being created from this class will

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have a followers attribute that set out to zero to begin with.