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Object-oriented programming is a very powerful model for reusing code.

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Let's take a look at how objects and classes are defined and used in Python.

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We'll start with this simpleoop.

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oop stands for Object-oriented programming.

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We'll make a working copy of this, and we'll go ahead and open the working copy.

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And let's just take a look at what's in here right now.

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This is a class, and a class, in Python, as in many object-oriented paradigms, a

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class is the definition that is used to create an object.

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It's sometimes called a blueprint.

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So objects are instances of classes.

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So when you take a class, here's the class that we've defined up here, class

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Fibonacci, and you assign it to a variable, that's called instantiating, or

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creating an instance, of that class,

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and the instance itself, in this case,

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it's just called f, that instance is called an object.

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An object is an instance of a class.

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So the class is the definition, and here we have class, and it's named Fibonacci,

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and it has these parentheses, and we'll talk later about what goes in the

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parentheses if anything. Right now nothing needs to go into them.

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The colon introduces the blocks or suites of code that are indented, and

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therefore part of the class definition.

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And here, we have two functions defined as part of this class.

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And each of these functions, you'll notice that its first argument is self.

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And here we have one that's just got self, and here we have one that's got self

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and some other variables.

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self is the common name for that first argument.

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It doesn't have to be self.

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It's traditionally self.

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And what it is is a reference to the instantiated object.

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So when we use the object f, and here we're calling a method or a function

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inside of the object f, that's what this dot notation does, f.series().

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It calls the series function or method, but it calls the copy of it that's part

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of the object, the instantiated object.

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And its first argument is actually a reference to the object f. And so, we can

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assign and use variables that are encapsulated within that object and that are

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actually carried around.

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So if we had different instances of the same class, they would have separate

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variables, separate values in self.a and self.b. This init function, or method, is

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actually special. This is called a Constructor.

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And this gets called when f gets assigned.

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So f gets assigned Fibonacci, and that creates an object called f, which is an

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instance of Fibonacci.

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As that object is created, init is called, and init is called with a reference to

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self and with these variables, and here we have 0 and 1.

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You can define these however you want to because you're writing this

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constructor. The constructor is optional.

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If you don't need it, you don't need to create it.

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But in this case, we used a constructor so that we could demonstrate how this works.

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And what this is doing here is it simply creating some default initial values

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for a and b, which are going to used as part of the Fibonacci series.

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And then we have this second method, or function, and this one is actually a

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generator. You see it uses the yield statement.

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And so that generates an iterator, which is used here in this for loop, and so

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for r in f.series() is going to give us a series of all the Fibonacci numbers

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that are less then 100.

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So let's go ahead and run it, and there we have our Fibonacci series up to 89,

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which is the last Fibonacci number that is less than 100.

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So here we have defined a class called Fibonacci, we have instantiated it,

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creating an object, called f, and in that object, we called this generator function

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and we got a series of Fibonacci numbers.

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So that is a simple example of a class and an object in Python.