Python OOP Tutorial (Object Orientated Programming ) - Overriding Methods

Key Takeaways

hey guys and welcome back to another object and classes tutorial video in today's video I'm gonna be going over loading default Python methods and why these are extremely useful now if you don't know what I'm talking about just stick around for one second and I will explain it so first of all I just want to talk about what I've already coded here I just have a very basic point class and you can see that our point object has three kind of attributes an X Y and then our coordinates which is self dot X and self dot Y we have very basic method that can simply move us by X and by Y when we type it in ok I've created four points down here and these are what we're going to use to kind of test up some examples and I'm about to create so in Python remember in my first video I was talking about the fact that if you create integer objects so for example I say like I equals five and like the Z equals five if I wanted to add these together all I simply have to do is well put a plus sign right and Python knows that this plus sign means okay these two things together now how does it know this and how does it know what to do well integers is pretty straightforward but what if we start doing things like strings right if you do S and then you go like six seven eight how but does Python know how to add these two strings together well it would make sense to it just appended on top but someone actually had to code this functionality in and that's exactly what we're gonna be doing in this video except with our custom point object okay and you'll see what I mean in just a second so pretty much what we want to eventually do at the end of this video is to be able to add multiply subtract in compare points without having to reference their attributes outside of the class so right now if I do p1 plus p2 our programs gonna crash because it doesn't know what that means but by the end of this video we're gonna be able to do that okay so that's what I'm gonna show you right now so in Python there's a bunch of defaults kind of operations and methods that you can apply on classes and by default that are not defined right on our point class if we try to add two things right now that doesn't make sense so what we're gonna do is add that method so to do this to add the add operation you're just going to do to find underscore underscore add okay and then in here you need to give another point object so what happens when I try to add a point and another point object well whatever we're going to return a new point okay that is simply equal to self dot X plus P dot X and then self dot y plus P del Y so what this is doing is since we're passing another point object so when we do like P 1 plus P 2 P 2 becomes P and P 1 becomes self so we're gonna grab the coordinates of P 1 add them to P 2 and return that in a new point object okay now the same works for subtract multiply and divide and for a few others as well so I'm just saying simply gonna copy this okay and paste it one more time and instead of add now you're probably guess I'm going to put sub and what this is going to do is allow us to subtract points so it's gonna be the exact same except now we are simply going to subtract the coordinates now with multiplication this one is simply defined underscore underscore mole underscore underscore and this going to allow us to use the asterisks or the star to multiply two different point objects so same thing it takes a point and in this case when we multiply points I could return a new point with multiplied coordinates but the way it actually works if you know anything about vectors is we're simply gonna return the scalar product which means you multiply the first two x-coordinates get a value in this case we get nine and then you actually add it to the y-coordinates multiplied together so in this case we'd have nine what do you call it plus eight and that would give us 17 we're not returning a new point object it's a scalar or like just a number value okay so we're gonna do here is we're gonna return self dot X multiplied by P dot X plus self-thought Y multiplied by P dot y and those are the three that I'm going to stick with right now and I'm gonna show you a bunch more that we can use to compare point objects using greater than equal then sign in just a second so I want to test if this is working so let's create a new point when say point five is equal to p1 plus p2 and I'm gonna say point six is equal to P for minus t1 okay and then we'll even go as far as creating p7 and applying p2 and p3 just to make sure everything's working so now I'm simply going to print to the screen p5 p6 and p7 and let's see what we get so you can see here I get main point object main point object and 9 now the way that this worked and the reason that we're not actually getting a coordinate value is because I have to show you another method that we can use so that this was actually gonna give us something meaningful because right now when we point printout our point objects right because 0.5 is a new point object because when we add point 1 and point 2 we are returned sorry a new point object right so if we want to make this meaningful and not just show us the address in memory where the point is stored which it currently is right now we need to add another method and this one is called STR okay what this is gonna do is this is going to be called every time we try to convert our point object into a string so when we try to print our point object it automatically looks for STR and if it doesn't find it it gives us this kind of gibberish right here but if it does find it it's simply going to well use the value that we returned so in this case we want to return I think we'd want to return from string probably the self dot coordinates right so I want it to look something like this we have brackets and then plus STR and then self dot X plus a comma plus STR self-thought Y and plus and then another bracket like this ok so now if I try to print point five point six at point seven you can see what we get and there we go so now instead of getting that gibberish we get 6 6 negative 3 and negative 3 now keep in mind you can make this anything you want but you do have to return a string value here for this to work ok so the next methods we're going to talk about I'm just gonna put them above string here just for good practice is going to be comparing two points so this is great now we can add we can subtract we can multiply but what if we want to compare so what if we want to see if point 1 is greater than 0.2 or if point 3 is greater than point well how do we do that we first have to determine how are we gonna compare points are we simply going to compare the exes and the Y's or are we gonna find like the magnitude of a point like what are we gonna do to compare which is larger in my case I want to find the length of a point from the origin so in this case the way this would work I think I can just bring up a little grid program here and just draw it for you quickly so if you have an origin like this okay I'm just using my mouse right now and you had a point here and a point here well from the origin this would have a distance and from the origin this would have distance obviously this could be like a distance of seven this could be a distance of two and seven would win right because we don't really care about the negatives if you had something all the way over here with a larger distance then what we would want that to win right so that's the way that we're gonna compare them and I'll talk about that and how we do that in one second so to compare we have four major comparisons I think that we can do and it goes I'll type down and we'll see so one of them is greater than and that is GT okay and you can do self and you also need another point object like this another one is greater than or equal to and greater than equal to simply GE okay and then the same thing we need P we have less than so define and you can probably guess LS or sorry LT what am I saying less then and then we also have less than or equal to so L II like that and we have one more and this is simply equal to so this is if we do the double equal sign then it's going to give us a comparison now in these methods we need to return a true or a false value so n greater then remember the way I said I wanted to compare them is to get like the magnitude of the point from the origin so I'm just gonna add a method in here I'm just gonna call it let's do length maybe okay and then in here I'm simply actually we don't need to take anything we're just going to return the math dot sqr T and I'm gonna import math right up here and this is simply how you get the length from the origin okay of self dot X ^ 2 + on again self dot why should the exponent - and this is gonna give us the length okay so import length so when I'm doing greater than I want to see if return self thought X first what am I saying self thought length is greater than P dot length like this okay and I believe we do actually need these square brackets here so all this is going to do is it's a boolean condition it says well if the length of our self is greater than the other length we'll then we're simply greater than so let's just copy this and put it in here and in this case we're just going to be greater than or equal sign because this is greater than or equal to copy this again change this around to less than and one more time and this is now just gonna be less than or equal to now if we're seeing if two things are equal to each other well that's pretty easy as well all we can do is simply take this or actually the way we're going to do this is just see if the coordinates are the same because if we try doing the math dot square root and we get like a large decimal number sometimes decimals kind of mess up in Python and they don't get the same precision so let's just return if self-thought x equals equals P dot X and self dot y equals equals P del Y because that would mean that they are at the same point right okay so let's do some comparisons now so let's just simply print if P 1 equals equals P 2 and then we'll print if p1 is greater than p2 and we can print if P 4 is less than or equal to p3 okay and just test these out okay so we get false true and true and you guys are welcome to mess around with these and kind of figure those out for yourself so I will show you I'm not going to go through all the methods because there's a lot of ones that you can overload but I'll show you how you can have a look at all of the different methods okay so I'm just gonna pull up a web page here that has like a large list of all of the kind of built-in methods that you can override or like what'd he call it overload there is a way in Python to like see all of them in print to the screen but I completely forget the command so I apologize when you guys knows that command please let me know in the comments because I've been looking for it I can't find it but anyways you can see here there's a ton like I think there's like a hundred or something of built-in ones that you can use like add sub mold if true to Florida can read through here and see what they all do some useful ones I will mention is probably Len I probably should have talked about that one but it's if you call the Len function on something so actually I'll show you Len really quickly just because I feel like I should have talked about so instead doing length here I could have just done define underscore underscore Len underscore underscore and what this would have done now is if I call like Len of p1 it's just gonna return whatever value I have here so mapped on square root okay that's like a really useful one too so I don't know why I didn't talk about that but anyways so I'll go back to this page for one second you can see real numbers slice slice can be useful if you're dealing with kind of like list objects that you're creating items and slices you can go through all these and kind of read them yourself I'm not going to talk about all of them because I'm sure these you guys probably want to end up using very much the ones that are very important are the ones I talked about so yeah so you can see built-ins like there's something you can do with like their built-ins to see them all alright and yeah I'll leave this link in the description in case any of you guys are interested in having a look at these but there is some way in Python again if you know that way please let me know ok guys so that's been it for this video in the next video I'm gonna be talking about static and class methods and then in the future video I'm gonna be talking about private private and public classes in Python so if you guys enjoyed the video please make sure you leave a like and subscribe and I'll see you again in the next one [Music]