Python Tutorial - 18. Inheritance

hello and welcome to Cod Basics coding tutorial today we are going to cover a fun topic called inheritance and here is the list of items we are covering in this video okay let's understand inheritance by taking the example of vehicle when you think about Vehicles you have uh so many vehicles available for use such as car trucks motorcycle Etc but they provide a same purpose which is transportation and when it when you go to specific type of vehicles such as car and motorcycle uh they have their own purposes and own characteristic for example our car has four wheels it has no roof it has a roof whereas motorcycle has only two wheels and it has got no roof car also has specific usages such as commute to work and vacation with family whereas motorcycle is primarily used for road trip and racing so as shown in this diagram both of these vehicles cars and motorcycle can be thought of as subclasses of a base class called vehicle and they share the same properties of a vehicle class which is to provide transport ation but on top of that same shared property they have their own specific characteristics and purposes such as Wheels roof difference and specific usages so here you can say that we have derived car and motorcycle subclass from a class vehicle or you can also say that these two classes inherit from a vehicle class so that's essentially the definition of inheritance here now what we're going to do next is we are going to implement this same example in Python so I have a python uh py Cham code editor open here and I'm going to write uh our first class which which is vehicle now if you remember from my last video uh the way you write classes is using a class keyword followed by the name of the class and column and then you start typing your uh methods so here I'm going to create one method in my vehicle class which is the general usage and the general usage is I'm going to say okay the general use of vehicle car vehicle class is to provide Transportation now I'm going to derive my first subass called car from vehicle and the way you inherit a class from another class is by writing the name of that class in in bracket like this so here it means my car class is derived from vehicle class or it's inherited from a vehicle class here I'm going to write an init method which is same as a Constructor and the first thing I'm going to do is I'm going to say okay I am car okay and I'm going to now Define certain properties such as wheel is 4 and has roof equal to True okay the second method I'm going to write is specific usage so car has got some specific usage uh which is uh commute to work vacation with family Etc okay so this is how I derive my class from another class okay now let's let's write our second class which is motorcycle and this is again deriv from a vehicle class and I'm it's essentially I'm just going to copy this code here and here I'm going to say okay I'm M motorcycle and the specific use will be different than that of the car and the specific use here is road trip and racing okay so we just derived two classes motor and car from vehicle now let's create some objects of it and let's try to realize like what real benefit this inheritance thing is giving us so the first object is the car object so I'm going to say C is equal to car and first print c. General Usage Now notice that car class doesn't have a method called General usage and still I can call that method why because I have inherited that method from vehicle class here here since this vehicle since this car class is derived from vehicle class I have an access to use all the methods and properties from my parent class okay so think about this being a parent and these two are its children okay so C do General usage and C do specific usage okay now let's first execute this and see what happens so when I run this here it is saying I'm am car so when I created the class object here it executed this Constructor and that's why it is saying I am car then the second thing I did is c. General usage so c. General usage was Transportation so as you see here it says general usage transportation and that's what it printed here and when I say c. specific usage it is going to print the specific usage as shown here which is commute to work and vacation with family so you can confirm that that's what it printed okay now let's create a an object of class motorcycle so here I'm just creating an object of motorcycle class and again I'm going to print the general usage and the specific usage so when I run this what happens here is it says I'm motorcycle my general usage is transportation and my specific use is road trip and racing okay so key takeaway from this exercise is you can call a method or a property on your from your parent class using the object of your derived class so these car and motorcycle are derived classes C and M are objects of derived classes and using those objects I calling this General usage method of my parent class and then you can call the specific methods from those sub classes now if you don't want to call this usage property um method explicitly you can call that within uh your specific usage um specific usage method so here in specific usage method I can say self. General usage so remember self is an object of car class and since it is derived from vehicle you'll be able to call General usage here and same thing you can do in motorcycle class self. General usage okay so here I'm creating an instance of car and motorcycle class and just calling specific usage method so if I execute this I get the same output as what we saw previously so it calls specific usage meth uh method then it comes here it calls General usage method which is this guy and then it calls the specific usage code okay that was that that was a simple way to illustrate inheritance using vehicle uh example if you have any doubts or any questions please post in the comments uh below uh the next uh topic next section we covering is the benefits of inheritance the there are three primary benefits of inheritance number one is code re reuse as you saw in this example of vehicle you can reuse the code of your parent class so let's say uh when you're programming in Python and someone has return a class already and you want to use all the code in that class but on to on top of that you want to do some customizations of your own then using inheritance you can do that easily that's why it provides a code reuse the second benefit is extensibility uh and it kind of overlaps with this first benefit that we just talked about uh in vehicle example we extended our vehicle class to derive new classes such as Scar and motorcycle the third benefit is readability uh it provides a very nice structure to your program especially when you're writing a big program you want your your code to be such that it remains readable because if the code is simple few lines it's easy to read but if the code is less million line of code it's very hard to read it uh for troubleshooting purpose and for developing new features uh using inheritance you will be able to gain this readability as it will provide a nice and uniform structure to your program okay one last thing we want to quickly cover is is is instance and is subass methods so here uh in the same example what I'm going to do is uh so I just created two class objects I'm I'm not going to call any method here uh so I have car instance and motorcycle instance and let me first call is instance method so is instance is a built-in function available in Python and what it will do is it will tell you if an object is an instance of a specific class or not for example here C is an instance of our car class so when I run this and let me just print this okay when I run this uh it is saying I'm car I'm motorcyle true so this the execution of this resulted into true which means C is indeed an object of class but if I do motorcycle here it will say false because C is not an object of motorcycle class okay so that is is instance now there is another method called e subplus what it means is if car is a subass of vehicle or not so you want to figure out if one class is a subass of another then just use is subclass Method when you run this you get true because car is a subass of vehicle but if I say car is a subass of motorcycle then it's going to print false because car is not derived from motorcycle you know car is more like a sibling of motorcycle uh it's not a child of MOT motorcycle okay so that was all about inheritance thank you for watching