Python/C4/Getting-started-with-functions/English-timed

Time	Narration
00:01	Hello friends and welcome to the tutorial 'Getting started with functions'.
00:05	At the end of this tutorial, you will be able to, Define a function. Define functions with arguments. Learn about docstrings. Learn about function return value. Read code.
00:16	Before beginning this tutorial,we would suggest you to complete the tutorial on "Conditionals" and "Loops".
00:22	While writing code, we always want to reduce the number of lines of code, and functions is a way of reusing the code.
00:32	Thus the same lines of code can be used as many times as needed.
00:35	A function is a portion of code within a larger program that performs a specific task and is relatively independent of the remaining code.
00:43	Now let us get more familiar with functions,
00:48	Consider a mathematical function f of x = x square.
00:53	Here x is a variable and with different values of x the value of function will change.
00:58	When x is one, f(1) will return the value 1 and f(2) will return us the value 4.
01:05	Let us now see how to define the function f of x in python.
01:10	Start your ipython interpreter by typing,ipython in command line.
01:17	Let us define our function f of x
01:19	So type def f within bracket x colon return x star x
01:29	Star denotes multiplication
01:34	Well that defined the function, so before learning what we did let us see if it returns the expected values, try,
01:45	f(1) f(2)
01:52	Yes, it returned 1 and 4 respectively.
01:55	And now let us see what we did.
01:58	We wrote two lines: The first line def f of x is used to define the name and the parameters to the function, and the second line is used to fix what the function is supposed to return.
02:12	def is a keyword and f is the name of the function and x the parameter of the function.
02:19	Pause the video here, try out the following exercise and resume.
02:24	Write a python function named cube which computes the cube of a given number n.
02:31	Switch to your terminal for solution.
02:33	The problem can be solved as,
02:36	In the terminal type def cube within bracket n colon return n star star 3
02:48	Let us check whether our function returns the cube of a number or not
02:53	So type cube within bracket 2 and hit enter.
03:00	It returned 8,which means we have defined our function,the right way.
03:05	And now let us see how to write functions without arguments.
03:09	let us define a new function called greet which will print Hello World .
03:15	So type def greet() colon and hit enter.
03:26	Then type print within double quotes Hello World exclamation
03:39	now we call the function as,greet() and hit enter.
03:45	Well that is a function which takes no arguments.
03:49	Also note that it is not mandatory for a function to return values.
03:53	The function greet neither takes any argument nor returns any value.
03:57	Now let us see how to write functions with more than one argument.
04:03	Pause the video here, try out the following exercise and resume the video.
04:08	Write a python function named avg which computes the average of a and b .
04:16	Switch to terminal for solution.
04:19	Type def avg within bracket a comma b colon return within bracket a + b divided by 2
04:36	For division we use slash.
04:42	Let us test our function,
04:44	Type on terminal avg within bracket 20 comma 30 and hit enter.
04:53	We get the correct average, 25.
04:56	Thus if we want a function to accept more arguments, we just list them separated with a comma between the parenthesis after the function's name in the def line.
05:06	It is always a good practice to document the code that we write, and for a function we define, we should write an abstract of what the function does, and that is called a docstring.
05:19	Let us modify the function avg and add docstring to it.
05:24	Do the following,
05:25	So now in the terminal type def avg within bracket a comma b colon
05:38	Then in triple double quote you can type avg takes two numbers as input (a & b), and returns the average of a and b
05:50	Then type return within bracket a+b and hit enter
06:02	Note that we have a syntax error.
06:09	The error that we saw here is because of indentation error in return(a+b)/2
06:15	So just input that command again.
06:25	So type def avg within bracket a comma b colon """ avg takes two numbers as input (a & b), and returns the average of a and b""" return within bracket a+b divided by 2
06:45	Note that docstrings are entered in the immediate line after the function definition and put as a triple quoted string.
06:55	And here as far as the code functionality is concerned, we didn't do anything.
07:00	We just added an abstract of what the function does.
07:03	Now try this in the ipython interpreter.
07:07	Type avg and question mark.
07:12	It displays the docstring as we gave it.
07:16	Thus doc string is a good way of documenting the function we write.
07:21	Now type f question mark and hit enter.
07:29	It does have a doc string associated with it.
07:37	Sorry It does not have a doc string associated with it.
07:40	Also we cannot infer anything from the function name, and thus we are forced to read the code to understand about the function.
07:48	Pause the video here, try out the following exercise and resume the video.
07:54	Add doc string to the function f.
07:59	We need to define the function again to add doc string to the function f and we do it as,
08:06	def f within bracket x colon
08:13	"""Accepts a number x as argument and, returns the square of the number x."""
08:24	Then type return x star x
08:32	Let us solve one more exercise
08:34	Pause the video here, try out the exercise and resume the video.
08:41	Write a python function named circle which returns the area and perimeter of a circle given radius r .
08:52	Switch to the terminal for solution.
08:57	The problem requires us to return two values instead of one which we were doing till now.
09:03	We can solve the problem as,
09:05	So now we can type in terminal def circle within bracket r colon """returns area and perimeter of a circle given radius r""" pi = 3.14 area = pi star r star r perimeter = 2 star pi star r return area comma perimeter and hit enter.
10:04	A python function can return any number of values.
10:07	There is no restriction for it.
10:09	Let us call the function circle as,
10:12	Typing it on terminal a comma p = circle within bracket 6 print a print p
10:39	Now we have done enough coding, let us do some code reading exercise,
10:46	Pause the video here and try to figure out what the function what does.
10:54	def what within bracket n colon
10:58	if n less than 0 colon n = -n while n greater than 0 colon
11:08	if n modulo 2 == 1 colon
11:12	return False
11:14	n slash = 10
11:19	And the next line is return True
11:23	continue from paused state It will return true if n modulo 2 is not equal to 1 and will return false, otherwise.
11:36	The function here returns True if all the digits of the number n are even, otherwise it returns False .
11:45	Now one more code reading exercise,
11:51	So it is given def even underscore digits within bracket n colon """returns True if all the digits in the number n are even, returns False if all the digits in the number n are not even"""
12:13	Then next line if n less than 0 colon n = -n while n greater than 0 colon
12:24	The next line if n modulo 2 == 1 colon return False n slash= 10 return True
12:40	Pause here and figure out what the function what does.
12:48	def what within bracket n colon
12:52	i = 1 while i star i is less than n colon
12:59	i += 1
13:02	return i star i == n comma i
13:07	continue the video The function returns two values.
13:11	One it returns the result of the while statement whether true of false, and second it prints the value that ii` currently holds.
13:23	Here, the function True returns and the square root of n if n is a perfect square, otherwise it returns False and the square root of the next perfect square.
13:37	So we look at that
13:40	def is underscore perfect underscore square within bracket n colon """returns True and square root of n, if n is a perfect square, otherwise returns False and the square root of the next perfect square""" i = 1 while i star i less than n colon i += 1 return i star i == n comma i
14:14	This brings us to the end of this tutorial.
14:17	In this tutorial, we have learnt to, 1. Define functions in Python by using the keyword def .
14:22	2. Call the function by specifying the function name.
14:25	3. Assign a doc string to a function by putting it as a triple quoted string.
14:33	4. Pass parameters to a function.
14:37	5. Then Return values from a function.
14:39	Here are some self assessment questions for you to solve
14:42	1. What will the function do?
14:46	def what(x)
14:48	return x star x
14:50	Returns the square of x
14:52	Returns x
14:54	Function doesn't have doc string
14:57	Error
14:59	1. How many arguments can be passed to a python function? None One Two Any
15:07	1. Write a function which calculates the area of a rectangle.
15:12	Now we look at the the answers,
15:14	1.The function will result into an error due to the use of wrong syntax in defining the function.
15:27	The function line should always end with a colon
15:32	Any number of arguments can be passed to a python function.
15:37	As we know, area of a rectangle is product of it's length and breadth.
15:41	Hence, we define our function as,
15:42	def area within bracket l comma b colon
15:47	return l star b
15:51	Hope you have enjoyed this tutorial and found it useful.
15:55	Thank you!

Contributors and Content Editors

Gaurav, Minal, PoojaMoolya, Sneha