How to Create Functions in Python! Beginner Lesson

what's going on you guys welcome back to the channel and today's video is going to be taking a look at how to define and call functions in python [Music] so the basic idea of a function in python is that you are grouping a certain amount of code that you may want to reuse over time with different variables leading to a different result and so whereas in python say you just had two numbers and you wanted to add them together it you're allowed to say like sum equals one plus two okay and if you run this code it's going to store the value of three in the sum and you can test that by using print and saying well just print out the sum okay and so if i run this you can see i get three and that's great a lot of you who are familiar with variables even know that you could make two variables like number one equals five and number two oops number two equals ten and then you could set sum equal to number one and plus number two um so there we go and then if i print some now you'll see it's 15. i can update the value of sum just by updating number one and number two in these variables but what you've done here is is you have technically written a function but you haven't grouped it in any sort of way where it's can be called from the outside world and so we're going to take a look at how to do that using a few different examples in python in this video and one of them will actually we'll start with some so let's go ahead and just take a look at how you create a function first thing is you do d e f which is define and essentially that's python shorthand for define a function and we'll call it sum so we'll say define sum and then you always put these parentheses when you're creating a function and what goes inside those parentheses is what variables are getting passed in so there are a couple ways to write almost every function a lot of the time you can create some of the code inside of it without needing to pass any variables in we'll take a look at two different ways to do this sum so let's say just like we've had it written here let's say you're passing in two numbers so we're gonna pass two numbers in and then you put a colon and tabbing is very important in python so if you're unfamiliar with object-oriented programming or python specifically you want to make sure that your one tab level in side of any function inside any if or while loop or anything like that that's just general python knowledge but then what you do to get data back from python inside of a function is you use the return and so in the case of a sum function we're going to do number one plus number two and that's basically saying what we want to return is the sum of these two numbers you could also use an intermediate variable if you wanted to you could say you know sum equals just like we did on the outside and sum equals this number one plus number two and then you could return the sum uh this maybe is a little bit cleaner to look at it may be um for you as a beginner programmer maybe this just helps you order your brain a little bit better um but i'm gonna go ahead and put it back the other way because this is um just the shortest fastest way to return the sum of two numbers now of course you wouldn't probably write a function uh just for adding two numbers together you would add some more levels to it which we'll take a look a little bit later in the uh a little bit later in the video and how to kind of create some more useful examples with these functions but okay so now the thing that um really people i think want to know is how do you call a function once you've created it so we've created this sum function that's great but it it hasn't really um it hasn't really done anything you'll see if i if i run this it actually won't give me anything because just writing the function doesn't do anything it's not being called so what you have to do to call a function is you have to type in the name of the function and then the parentheses and then you put some variables inside of it so let's just start with 2 and 3 as our two numbers and we'll see it runs but we're not printing anything because there's no display inside of the function so if we print the sum then now when it returns the number one plus number two that's what's going to be executed here and then we're going to print that onto the console so there you see we run it we get five and that's pretty cool this can be coupled essentially like let's say we want to write this entire program just for the purpose of summing two numbers you could you could say num1 equals integer input and if you're completely confused by this input print formatting i suggest you go back to the learn python for beginners tutorial series that's on this channel and it'll go from everything from downloading and installing python to how to get user input how to use type conversions and things that you're seeing in this video so i'm trying to go kind of slow and explain everything as i do it but there are concepts that you can get elsewhere that will help you understand what's going on here but essentially if we said num integer input enter first number and what we're doing right now is we're prompting the user for those numbers and so this way you can see every time we run this function we are going to have the option as the user of actually generating a different sum based on our input so what i just did is i set up two inputs that are asking for the first and second number i'm storing those in these variables num1 and num2 we pass that into the function and you can see i intentionally gave them different names here in the outside world versus inside the function that is typically the best practice because if i were to use num1 in here it's even gonna recommend hey this shadows the name from the outside scope essentially like you named it something in here it will work in here if you want it to but it could get really confusing if you look at your program or your debugging and you have num1 num2 in multiple locations so i recommend using different names for your variables when you create them in the outside world versus inside of your function but let's go ahead and run this so enter first number i'm gonna go with five enter second number go with another five and it prints a 10 out on the screen so right there that's just kind of a crash course in how to call a function now let's say we put this prompting inside of the function okay because i think i mentioned earlier you can create a function that doesn't have any variables so let's say we put when you call summation we also want to gather the user info inside of that function then all we would do when we call this function now is we just say sum and then empty brackets and now it should operate exactly like the way we just ran it so you just saw us run the function it asked you for two numbers and then it returned the sum this is probably actually the better way to create this program where if you were to design a function and then hand it off to someone else on your team and say all you have to do is run the function and we'll handle gathering user input everything else it's it's a complete solution just in its own this is probably the better way to do it because now you'll see when we run it enter first number five enter second number 12 and we get 17 back but the difference is all someone that you gave this to would have to do is run you know some and they wouldn't have to know that they also have to add a few input lines of code and so one more thing because i put the function inside of print for that purpose of displaying the result but typically if you want to get the result of something back so let's say we ran the sum function we wanted to put a local variable that was like um i'll just call it local sum okay so we could then use local sum as any as anything um we want and modify it and and increment it and use it later on in our program as much as we want so we could say local sum plus five uh for for whatever reason and let's go ahead and just uh print that out so now what we're gonna do is when i run this program it's going to come down here it's gonna see oh i have to run the sum function to put a number inside local sum but then what we're actually going to display on the screen is that result plus 5 that we modified um so so this will be kind of an interesting explanation of how functions can get called but let's say right now we're running the sum function so we did 12 plus 6 which is 18 but then we came down and we added 5 to it so another another way of maybe explaining that is if we did a local sum 2 that was also equal to the sum function and then what we're going to print out is local sum 2 plus local sum 1. so this is kind of this may be kind of silly maybe what would make sense is if we had done subtraction or something there but okay we did 12 plus 9 it stored that value in the variable local sum and we're running it again so let's do 90 plus 1. and what it just did is it added 21 which was the first local sum to 91 for 112 so that's just a way of showing how you can create and call functions as well as how to store the return value from those functions inside of a variable as well as how you can use and manipulate that variable later on in your program so this was a basic python tutorial i hope you found it useful certainly a lot of the videos on this channel do build on these concepts and kind of expand it to more cool things one of the first videos i did using a lot of functions was creating a four function calculator in python where we gather what operation a user wants to do whether it's division multiplication subtraction and processes your inputs based on what you've entered and that uses a lot of calling functions and returning outputs based on those functions so that would kind of be the logical next step in your learning i recommend checking that video out if you have more interest if you got confused about anything or there's something specific you want to see on the channel just let me know about in the comments below i'll get back to you as soon as i can or possibly make a video on it i hope you found this useful i really appreciate a like to the video subscribe to the channel if you did it helps me out a ton with the youtube algorithm and as always good luck with your code and thanks for watching thanks bye