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

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(Created page with '{| border=1 !Visual Cue !Narration |- | 0:01 | Hello friends and welcome to the tutorial 'Getting started with functions'. |- | 0:05 | At the end of this tutorial, you will be …')
 
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| We wrote two lines: The first line <tt>def f of x </tt> 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.  
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| 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.  
  
 
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| <tt>def</tt> is a keyword and <tt>f</tt> is the name of the function and <tt>x</tt> the parameter of the function.
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| '''Write a python function named <tt>cube</tt> which computes the cube of''' a given number n.
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| '''Write a python function named cube which computes the cube of''' a given number n.
  
 
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| let us define a new function called <tt>greet</tt> which will print <tt>Hello World</tt>.
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| Write a python function named <tt>avg</tt> which computes the average of <tt>a</tt> and <tt>b</tt>.
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| 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 <tt>def</tt> line.
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| Let us modify the function <tt>avg</tt> and add docstring to it.  
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| We need to define the function again to add docstring to the function <tt>f</tt> and we do it as,
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| We need to define the function again to add doc string to the function   f and we do it as,
  
 
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| '''Write a python function named <tt>circle</tt> which returns the''' area and perimeter of a circle given radius <tt>r</tt>.
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| '''Write a python function named circle which returns the''' area and perimeter of a circle given radius r .
  
 
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| Pause here and try to figure out what the function <tt>what</tt> does.
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| <nowiki>if n less than 0 colon n = -n while n greater than 0 colon</nowiki>
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| continue from paused state It will return true if <tt>n modulo 2</tt> is not equal to 1 and will return false, otherwise.
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| continue from paused state It will return true if n modulo 2 is not equal to 1 and will return false, otherwise.
  
 
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| The function here returns <tt>True</tt> if all the digits of the number <tt>n</tt> are even, otherwise it returns <tt>False</tt>.
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| Pause here and try to figure out what the function <tt>what</tt> does.
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| Here, the function returns <tt>True</tt> and the square root of <tt>n</tt> if n is a perfect square, otherwise it returns <tt>False</tt> and the square root of the next perfect square.
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| Here, the function returns True 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.
  
 
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| In this tutorial, we have learnt to, 1. Define functions in Python by using the keyword <tt>def</tt>.
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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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| 3. Assign a docstring to a function by putting it as a triple quoted string.
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Revision as of 16:13, 28 March 2013

Visual Cue Narration
0:01 Hello friends and welcome to the tutorial 'Getting started with functions'.
0:05 At the end of this tutorial, you will be able to,
  1. Define a function.
  2. Define functions with arguments.
  3. Learn about docstrings.
  4. Learn about function return value.
  5. Read code.
0:16 Before beginning this tutorial,we would suggest you to complete the tutorial on "Conditionals" and "Loops".
0:22 While writing code, we always want to reduce the number of lines of code, and functions is a way of reusing the code.
0:32 Thus the same lines of code can be used as many times as needed.
0:35 A function is a portion of code within a larger program that performs a specific task and is relatively independent of the remaining code.
0:43 Now let us get more familiar with functions,
0:48 Consider a mathematical function f of x = x square.
0:53 Here x is a variable and with different values of x the value of function will change.
0:58 When x is one, f(1) will return the value 1 and f(2) will return us the value 4.
1:05 Let us now see how to define the function f of x in python.
1:10 Start your ipython interpreter by typing,ipython in command line.
1:17 Let us define our function f of x
1:19 So type def f within bracket x colon 
        return x star x
1:29 Star denotes multiplication
1:34 Well that defined the function, so before learning what we did let us see if it returns the expected values, try,
1:45 f(1) 
f(2)
1:52 Yes, it returned 1 and 4 respectively.
1:55 And now let us see what we did.
1:58 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.
2:12 def is a keyword and f is the name of the function and x the parameter of the function.
2:19 Pause the video here, try out the following exercise and resume the video.
2:24 Write a python function named cube which computes the cube of a given number n.
2:31 Switch to your terminal for solution.
2:33 The problem can be solved as,
2:36 In the terminal type def cube within bracket n colon 
                     return n star star 3
2:48 Let us check whether our function returns the cube of a number or not
2:53 So type cube within bracket 2 and hit enter.
3:00 It returned 8,which means we have defined our function,the right way.
3:05 And now let us see how to write functions without arguments.
3:09 let us define a new function called greet which will print Hello World .
3:15 So type def greet() colon and hit enter.
3:26 Then type print in double quotes Hello World exclamation
3:39 now we call the function as,greet() and hit enter.
3:45 Well that is a function which takes no arguments.
3:49 Also note that it is not mandatory for a function to return values.
3:53 The function greet neither takes any argument nor returns any value.
3:57 Now let us see how to write functions with more than one argument.
4:03 Pause the video here, try out the following exercise and resume the video.
4:08 Write a python function named avg which computes the average of a and b .
4:16 Switch to your terminal for solution.
4:19 Type def avg within bracket a comma b colon 
     return  within bracket a + b divided by 2
4:36 For division we use slash.
4:42 Let us test our function,
4:44 Type on terminal avg within bracket 20 comma 30 and hit enter.
4:53 We get the correct average, 25.
4:56 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.
5:06 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.
5:19 Let us modify the function avg and add docstring to it.
5:24 Do the following,
5:25 So now in the terminal type def avg within bracket a comma b colon
5:38 Then in triple double quote you can type avg takes two numbers as input (a & b), and returns the average of a and b
5:50 Then type return return within bracket a+b divided by 2
6:02 Note that we have a syntax error.
6:09 The error that we saw here is because of indentation error in return(a+b)/2
6:15 So just input that command again.
6:25 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

6:45 Note that docstrings are entered in the immediate line after the function definition and put as a triple quoted string.
6:55 And here as far as the code functionality is concerned, we didn't do anything.
7:00 We just added an abstract of what the function does.
7:03 Now try this in the ipython interpreter.
7:07 Type avg and question mark.
7:12 It displays the docstring as we gave it.
7:16 Thus doc string is a good way of documenting the function we write.
7:21 Now type comma f question mark and hit enter.
7:29 It does have a doc string associated with it.
7:37 Sorry It does not have a doc string associated with it.
7:40 Also we cannot infer anything from the function name, and thus we are forced to read the code to understand about the function.
7:48 Pause the video here, try out the following exercise and resume the video.
7:54 Add doc string to the function f.
7:59 We need to define the function again to add doc string to the function f and we do it as,
8:06 def f within bracket x colon
8:13 """Accepts a number x as argument and, returns the square of the number x."""
8:24 return x star x
8:32 Let us solve one more exercise
8:34 Pause the video here, try out the following exercise and resume the video.
8:41 Write a python function named circle which returns the area and perimeter of a circle given radius r .
8:52 Switch to the terminal for solution.
8:57 The problem requires us to return two values instead of one which we were doing till now.
9:03 We can solve the problem as,
9:05 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 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 try to figure out what the function what does.
12:48 def what within bracket n colon
12:52 i = 1 while i star i les than n colon
12:59 i += 1
13:02 return i star i == n comma i
13:07 continue from paused state 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 returns True 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. 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 And 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

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