Difference between revisions of "Python/C4/Getting-started-with-functions/English-timed"

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| At the end of this tutorial, you will be able to,
 
| At the end of this tutorial, you will be able to,
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Define a function.
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# Define a function.
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Define functions with arguments.
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# Define functions with arguments.
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Learn about docstrings.
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# Learn about docstrings.
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Learn about function return value.
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# Learn about function return value.
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Read code.
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# Read code.
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|01:19
 
|01:19
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|So type def f within bracket x colon
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|So type def f within bracket x colon   return x star x
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        return x star x
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|f(1)
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|f(1) f(2)
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f(2)
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|02:36
 
|02:36
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|In the terminal type def cube within bracket n colon
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|In the terminal type def cube within bracket n colon return n star star 3
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                      return n star star 3
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|04:19
 
|04:19
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|Type def avg within bracket a comma b colon
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|Type def avg within bracket a comma b colon return  within bracket a + b divided by 2
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      return  within bracket a + b divided by 2
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| Do the following,
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| Do the following,So now in the terminal type def avg within bracket a comma b colon  
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|So now in the terminal type def avg within bracket a comma b colon  
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|So type def avg within bracket a comma b colon
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|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
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  """ avg takes two numbers as input (a & b), and
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returns the average of a and b"""
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return  within bracket a+b divided by 2
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|So now we can type in terminal  
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|So now we can type in terminal def circle within bracket r colon """returns area and perimeter of a circle given radius r"""
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  def circle within bracket r colon
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pi = 3.14
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"""returns area and perimeter of a circle given radius r"""
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area = pi star r star r
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pi = 3.14
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perimeter = 2 star pi star r
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area = pi star r star r
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return area comma  perimeter and hit enter.
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perimeter = 2 star pi star r
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return area comma  perimeter and hit enter.
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|Typing it on terminal a comma  p = circle within bracket 6
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|Typing it on terminal a comma  p = circle within bracket 6. print a, print p
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print a
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print p
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|So it is given def even underscore digits within bracket n  colon
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|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"""
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"""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"""
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|The next line if n modulo 2 == 1 colon return False n slash= 10 return True  
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return False
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n slash= 10
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return True  
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|def is underscore perfect underscore square within bracket  n colon
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|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  
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"""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
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i += 1
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return i star i == n comma  i  
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| In this tutorial, we have learnt to, 1. Define functions in Python by using the keyword def  .
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| In this tutorial, we have learnt to, Define functions in Python by using the keyword def  .
  
 
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| 2. Call the function by specifying the function name.
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| Call the function by specifying the function name.
  
 
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| 3. Assign a doc string to a function by putting it as a triple quoted string.
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| Assign a doc string to a function by putting it as a triple quoted string.
  
 
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| 4. Pass parameters to a function.
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| Pass parameters to a function.
  
 
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| 5. Then  Return values from a function.
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| Then  Return values from a function.
  
 
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| 1. What will the function do?
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| What will the function do?
  
 
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| 1. How many arguments can be passed to a python function?
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| How many arguments can be passed to a python function?
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** None
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None
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** One
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One
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** Two
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Two
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** Any
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Any
  
 
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| 1. Write a function which calculates the area of a rectangle.
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| Write a function which calculates the area of a rectangle.
  
 
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| 1.The function will result into an error due to the use of wrong syntax in defining the function.  
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| The function will result into an error due to the use of wrong syntax in defining the function.  
  
 
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| Hence, we define our function as,
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| Hence, we define our function as, def area within bracket l comma b colon
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Latest revision as of 12:44, 27 March 2017

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,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, Define functions in Python by using the keyword def .
14:22 Call the function by specifying the function name.
14:25 Assign a doc string to a function by putting it as a triple quoted string.
14:33 Pass parameters to a function.
14:37 Then Return values from a function.
14:39 Here are some self assessment questions for you to solve
14:42 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 How many arguments can be passed to a python function?

None One Two Any

15:07 Write a function which calculates the area of a rectangle.
15:12 Now we look at the the answers,
15:14 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, 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

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