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what's up guys i'm punit from
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programmers and welcome back to this
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series on python
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in the last few videos we learned about
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decision making and loops
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we will start a new section today we
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have been using the term
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function a few times in our videos
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without explaining what they are
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in this video we will look into
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functions in detail and learn how to
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create them
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and why they are used so let's get
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started
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in programming a function is a group of
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related statements
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that performs a specific task they help
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us divide a large program
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into smaller chunks so that it's easier
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to understand
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and change suppose you need to create a
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program
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that draws circles and rectangles of
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different colors
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based on user input instead of creating
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one big chunk of statements to create
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this program
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we can create three functions to solve
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this first
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create a circle function then a
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rectangle function
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and then the color the shape function
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this helps us to divide complexity
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and we can focus on only a small part of
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the problem at one time
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now let's see how we can create a
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function in python
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to create a function we use the def
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keyword which stands for the function
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definition
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followed by the function name then i'll
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use the empty parenthesis
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followed by a column so i'll say def def
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greet empty parenthesis and column
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here we have defined a function name
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greet however
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this code will give us an error because
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the function body is missing
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let's fix that for now i'll only add two
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print statements as its body
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so i'll say print hello
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and then let me add another print
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statement print
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how do you do remember we need to use
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indentation to specify that this is the
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body of the function
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we have successfully created a function
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named greet now let me run this code
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and we don't really see anything this is
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because
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defining a function won't do anything in
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itself to bring the function into action
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we need to call it our function name is
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greet
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with empty parenthesis so to call it i
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will just use greet with empty
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parentheses
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so here i'll say greet
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and now when i press run then you can
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see that hello
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and how do we do are printed here's how
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this code works
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when we call the function the control of
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the program jumps to the function header
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then the statements inside the function
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are executed
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when this task is completed the control
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of the program
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goes back to the function call and the
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next statement
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after the function call is executed one
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thing with functions
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is that once we define a function we can
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call it any number of times
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let's call our greet function three
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times so here i'll say greet
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and one more greet and now if i press
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run
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as you can see the function has run
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three times that's why these two
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statements were executed
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one two and three times
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so if we need to perform a task again
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and again we can wrap the codes inside a
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function
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and use the function any number of times
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we just need to call the function again
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and again
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one thing to remember when we create a
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function is that we need to define a
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function
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first before we can call it this code
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for instance will not work
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let me run this code to show you
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here when the grade function is called
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python doesn't know that this function
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exists
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because it's defined after the function
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call so always remember to
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define a function before you use it
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before moving to the next section of the
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video i'd like to mention that the
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program is team has created an app that
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allows you to learn python from your
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phone
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the app contains bit size lessons that
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are easy to understand
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a built-in interpreter so that you can
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run python on your phone
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quizzes and many more features the app
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is available on both ios and android the
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links are in the video description below
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now let's talk about python arguments
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and how our greet function from the
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previous example
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can be changed to allow arguments
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suppose we want to make our greet
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function a bit more personal
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so instead of printing hello we want to
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print something like
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hello jack or whatever the person's name
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is
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in such cases we can pass values to a
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function
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these values we pass to a function are
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called arguments
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so i'll go back to the code that i
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started with i'll remove these two greet
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functions because i want only one
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and here inside the grid function i'll
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pass the jack string like this
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this value that we passed during a
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function call is called an
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argument so jack here is an argument
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and in the function definition i'll add
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a variable in the greet function
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i'll call it name
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this name variable accepts whatever
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value is sent as an argument during the
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function
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call in this case jack is transferred to
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the variable name
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now i can use the name parameter inside
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the function
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so now i can say hello comma
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name and when i press run then i get
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hello
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jack let's see step by step how this
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function works
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when we call the greet function with the
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argument jack
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then this is passed to the name variable
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inside the function definition then
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the statements inside the function are
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executed we can use the name parameter
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inside the body of the function
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when this task is completed the control
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of the program comes
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back to the place from where the
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function was called
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and the next statement is executed in
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this case there's nothing here
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it's also possible to pass multiple
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arguments to a function
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as per our needs if we need to pass
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multiple arguments to a function
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we can separate them by commas let's see
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this in action by creating a function to
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add two numbers
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so i'll remove the old code and i'll
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create a new function called add numbers
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so i'll say def
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add underscore numbers obviously i'll
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need two parameters
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n1 and n2 and then inside the function
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i'll say result
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equals n1 plus n2
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print the sum
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is and here i'll say result
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now outside the function i'll say number
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1
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equals 5.4 number two
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equals six point seven and then i can
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call
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add underscore numbers number one
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comma number two in this program
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we have passed number one and number two
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as arguments to the add numbers function
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these arguments will be accepted as n1
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and n2
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once they are passed to the add numbers
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function so inside the function
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n1 will be 5.4 and n2 will be 6.7
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then we have added the numbers and
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printed them inside the function itself
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let's run this code and see the output
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as you can see
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i now have the sum of those two numbers
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in our program to add two numbers we are
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finding the sum of numbers
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and printing it it's working fine
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however
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it's better just to find the sum inside
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the function
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and print the result somewhere else we
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can achieve that by using the return
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statement
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inside the function i'll remove this
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print statement
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and i'll say return
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result when we return a value
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it comes back to the function and we can
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assign this return value to a variable
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like this
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so here i can say result equals
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add numbers number one comma number two
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and i can print the result as
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print the sum is
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and then i can say result let's see step
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by step how this program works
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we call the add numbers function with
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two arguments
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number one and number two which are
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accepted by the function definition
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as n1 and n2 the sum of n1
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and n2 is calculated and the result
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is returned to the function call this
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return value
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is assigned to the result variable
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and in the next line we just print the
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result variable
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outside the add numbers function
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whenever a return statement is
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encountered inside a function
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the control of the program goes back to
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the place from where it's called
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let's see an example of this let's get
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back to our grid function that we wrote
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before
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i'm pasting it here
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when i press run then we get hello jack
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and how do you do here now let me modify
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this program a little bit
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i'll add a return statement after this
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line and let's see what happens
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now when i press run then you can see
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that only hello jack is printed
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this is because when the return
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statement is encountered
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immediately the function terminates and
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control of the program goes back to the
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place from where the function is called
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at this point we have covered all the
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basics to create a function
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these functions we created ourselves are
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known as user defined functions
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actually we have already used functions
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numerous times
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in all of our videos remember print it
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is also a function
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the function definition of this print
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statement is defined somewhere inside
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the python programming language
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that's why we can just call the function
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and it just works
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these functions defined inside of python
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are called built-in functions
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we have also used other built-in
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functions like float
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int input and so on in our videos
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there are numerous built-in functions
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available in python that make our life a
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whole lot easier
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for example suppose we have a list like
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this
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now if we need to find the length of
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this list we can use the len function
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so here i can say length
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equals len max
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and i can print the length of the list
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as print
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length is comma
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length let's run this code and see the
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output when i press run
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then as you can see it says length is 5
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which is the length of the number of
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items in this
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marks list if we instead needed to find
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the sum of the items of the list
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we don't need to manually write the code
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ourselves we can use the sum function
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that's available in python
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so here i can say marks underscore sum
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equals sum of marks
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and then i can print the sum as print
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the
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total marks you
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got is and then i can say
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marks underscore sum now when i press
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run
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then it says the length is 5 and the
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total marks you got is 308
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which is the sum of these marks if
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you're interested
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you can find all the built-in functions
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available in python in the
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programming.com website
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the link will be in the description
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below let's put all the things
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we have learnt in this video in action
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suppose you have just attended a
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university examination
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the marks you obtained in various
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subjects are stored in a list like this
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you want to find the average marks you
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obtained in the exam
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and based on the average marks you want
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to find your grade
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the grading rule is like this you will
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get grade a
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if the average marks is equal to or
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above 80
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you will get grade b if the average max
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is equal to or above 60
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and less than 80 you will get grade c if
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the average max is equal to or above
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50 and less than 60 and if the average
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marks is less than 50
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you will get great f to solve this
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problem
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we will create two functions one to find
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the average marks
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and another to compute the grade so
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let's get started
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i'll start with the function definition
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but before that let me add a little
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comment i'll say
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function to find average marks
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now let me define my function as def
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fine average marks now the argument to
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this
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will be a list of marks and inside i'll
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say
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sum of marks equals
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some marks i also need to find the
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number of subjects or the number of
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marks i have so i'll say total
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underscore subjects
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equals the length of this marks list
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and then now i can calculate the average
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as average
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underscore marks equals sum of
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marks divided by total subjects
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let me return this average marks
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variable
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and now outside the function i can say
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average
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marks equals find average
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marks i'll pass in the marks list and
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here i'll say
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print your average marks
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is and i'll say average underscore marks
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when i press the run button i can see
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that my average marks is 67.8
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which is the average of these five
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numbers which is calculated as sum of
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these numbers
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divided by the total number of subjects
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which is 5 in this case
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now we need to create another function
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to calculate the grade based on the
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average marks
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let's do that now i'll create another
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function but before that let me add a
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little comment
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i'll say calculate the grade and
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return it and then i'll say def
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compute underscore grade now the
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parameter or the argument to this will
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be the average marks
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so i'll say average marks and inside
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i'll say
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if average marks greater than
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equals 80 then grade
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is a alif
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average marks greater
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equals 60
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then the grade is b
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alif average max
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greater than equals 50 in this case
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the grade is c and the else clause
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i'll say grade equals f
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and outside the if block i'll say return
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grade now i can use this compute grade
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function as
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grade equals compute
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underscore grade average
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marks now let me print
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this grade as your grade is
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and the grade variable now when i press
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it on
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i can see that my average marks is 67.8
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and my grade is b which is not the best
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result but at least i now know what my
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grade is
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before we end this video here's a
00:15:32
programming task for you can you create
00:15:34
a program to add and multiply two
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numbers
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for this create two functions add
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underscore numbers
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and multiply underscore numbers these
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functions should compute the result and
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return them to the function call
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and the results should be printed from
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outside the function
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you'll find the answer to this question
00:15:52
in our github repository
00:15:54
also visit our website programmies.com
00:15:56
for more tutorials and examples
00:15:58
the links will be in the description
00:16:00
below now let's recap what we learned
00:16:02
a function is a block of code that
00:16:04
performs a specific task
00:16:07
we use the def keyword to define a
00:16:09
function
00:16:10
to bring the function into action we
00:16:12
need to call the function
00:16:14
we can call the same function as many
00:16:16
times as we want as per our needs
00:16:19
we can pass values to a function these
00:16:21
values
00:16:22
passed to functions are called arguments
00:16:24
or parameters
00:16:26
the return statement can be used inside
00:16:28
a function the return statement returns
00:16:30
a value
00:16:31
from a function and exits the function
00:16:33
as well that's it for this video
00:16:35
i hope you learned something if you're
00:16:36
just watching the video without writing
00:16:38
any code
00:16:39
i highly encourage you to try the
00:16:40
programs in this video on your own
00:16:42
the only way you can be a good
00:16:43
programmer is by trying
00:16:45
by the way you can find all the programs
00:16:47
from this video on github
00:16:49
i've provided the link in the
00:16:50
description below feel free to copy the
00:16:52
program and edit them as you please
00:16:54
and if you have any questions and
00:16:56
feedback use the comment section below
00:16:58
in the next video we will learn about
00:17:00
different types of function arguments in
00:17:02
python
00:17:03
join me in this video series and let's
00:17:05
explore the exciting world of
00:17:06
programming together
00:17:07
if you like this video hit the like
00:17:09
button now and also don't forget to
00:17:11
subscribe to our channel
00:17:12
and ring that bell icon so that you
00:17:13
don't miss the next video thanks for
00:17:15
watching and i'll see you in the next
00:17:17
one
00:17:17
happy programming
