Intermediate Python Tutorial #5 - Lambda Functions

hey guys and welcome back to the fifth video in my advanced Python programming tutorials in today's video I'm gonna be going over lambda I think that's the way you say it at least excuse me if I'm gonna say around in this whole video which pretty much stands for an anonymous function now these are extremely useful and they don't take up very much space in your program which is really good and I'm going to show you exactly how they work and what they do so I first wanted to start off by defining a regular function again this is one example I've been using a lot I'm just gonna say defined func say like return X plus 5 that's what our function is gonna do it's simply gonna add 5 to the number whatever we give it's alright if I print something like funk of - we should get 7 there we go and we get 7 to the screen now for an extremely basic function like this on oftentimes you don't want to have to write a function definition and take up like two lines of code like this it's easier to write it in a different way and it looks like more smooth maybe more slick in your program and I'm going to show you how to do that so that's one way that we can do it by making a function like that another way and this is using lambda is to do something like this so the name of our function I say func I'll say func - is equal to and then we're going to type our keyword lambda like this you can see it highlights in orange just like our definition key here for our function we're gonna give it a parameter or multiple parameters I think you can use multiple parameters at least and then we're simply gonna state what it returns so the way this works is you type lambda the parameter or multiple parameters which we're gonna try in a second a colon and then whatever value you're gonna return so the thing with lambda is it's used when you have one returned X or one expression in your function so something like this so again I can do return x plus 5 over 4 like I could do a whole expression as long as that expression fits on one line then that's perfectly fine to return and I'll show you how this works so if I say print func - and I just give a number like 9 there we go we get 14 and seven so it works just like a regular function and it kind of just looks like a variable so we're saying function two is equal to an anonymous function that's what lambda stands for an anonymous function with the parameter access simply gonna return X plus five now these are really useful for using with the map function and the filter function which I'm gonna show you later so you don't have to constantly create a new function up at the top of your program and you can also use them inside of other functions so let's let's start by doing that okay I guess a func to simply just gonna copy it and paste it into my other function and then I'm a return func two of x plus 85 let's try that and now if I call my function we can see that we get 92 like so now this again is really useful because you want to oftentimes create another function or use something multiple times within a function but you might not want to like write a new one up here like funk too you just want it to be only used within that function and in that case you would use lambda as it keeps it all contained and have to be top your function you can write a bunch of other many functions that you can then use multiple times within your program it's hard to see the use case for it in small examples like this but they are extremely useful especially in like more in-depth code longer code so now I'm going to show you with multiple parameters so I believe and I'm not sure but we'll see if we can do this so we're gonna try I'm going to make func three is equal to lambda X Y and then somebody to get returning X plus y so let's just see if we call fun and let's give it value like five and five and we'll print that to the screen as well see there we go so that does work as well so you can give this infinitely num an infinite amount of parameters just like you'd be able to do something like this in our function and you can also I believe do optional parameter so you do something like y equals four and then if I put five we should be getting a value of nine here and there we are so you can use optional parameters you can do everything that you'd be able to do with a regular function except you can just return one expression like that okay so let's now use this with our map function and our filter function so in earlier videos I used the map function and to recall what that does is going to create a list quickly say a equals one two three four five six seven eight nine oops nine and ten like that and I'm now just gonna say let's say new this equals list map and then we're gonna have a function in this case I'll just write func for now and then we give it a list right like okay so what I want to do now is I actually want to just put a function in here without having to create a new one up here like I don't want to define func so this is a perfect example where we can use the lambda we don't even have to make a variable like equal to the function anymore we can just type lambda right in here so lambda and there was so X and so X plus five so now we again should simply just be adding five to each of the elements in a and then practice over spread new listed screen now and see if this is indeed working and there you go we can see we start at one so six all the way up to 15 like so again that saves us now having to make a function at the top of our program that we're only gonna use for one specific case which is this map function I again we also don't have to create like func equals lambda up here what you can if you want if you're gonna use it in a different case you can just type it right in the same line as your map function or as your filled with your filter function so this works the same with the filter function of your filter like so it's gonna be our function I guess yeah I believe this works with the fields for me oh yes it does okay so what this is gonna do now is we're just going to return X modulus two equals equals zero so again now given X we're gonna see if it's divisible by two if it is we return true we add that element to the list otherwise we will not be check now we get two four six eight ten and there we go so you can see why lambda is extremely useful it's really cool especially if you want to create a lot of mini fun you want to create functions within functions and say keep everything nice and organized and it's a nice trick to be able to use in Python so with that being said that's been the end of the video today if you guys get in journey to learn something please make sure you leave a like and subscribe to the channel and I will see you again in the next tutorial [Music]