View source for Python/C4/Advanced-features-of-functions/English-timed

{| border=1
|'''Time'''
|'''Narration'''

|-
| 00:01
| Hello friends and Welcome to the tutorial on 'advanced features of functions'.

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| 00:06
| At the end of this tutorial, you will be able to,

# Assign default values to arguments, when defining functions.
# Define and call functions with keyword arguments.
# Learn some of the built-in functions available in Python standard library and the scientific computing libraries.

|-
| 00:23
| Before beginning this tutorial,we would suggest you to complete the tutorial on "Getting started with functions".

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| 00:32
| Let us Start the ipython interpreter in command 

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|00:36
|ipython hypen pylab in command

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| 00:43
| Let's use the  round  function as an example to understand what a default value of an argument means. 

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| 00:49
| Let's type the following expressions in the terminal.

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|00:52
|Type round within bracket 2.484 and hit enter.
Then type round  2.484 comma  2

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| 01:10
| Both the first expression and the second are calls to the round  function, but the first calls it with only one argument and the second calls it with two arguments. 

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| 01:22
| By observing the output, we can guess that the first one is equivalent to call with the second argument being 0. 0 .

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| 01:30
| '''s.strip() # strips on spaces.'''

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| 01:35
| s.strip within single quote at the rate  # strips the string of 'at the rate' symbols.

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| 01:47
| Thus it can be said that here, blank space is the default argument.

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| 01:52
| plot within bracket x comma  y # plots with x versus y using default line style. plot within bracket x comma  y comma  in single quote o # plots x versus y with circle markers.

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| 02:14
| Hence, here when third argument is not provided, it shows default line style.

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| 02:20
| linspace within bracket 0 comma  2 star pi comma  100 # returns 100 points between 0 and 2pi linspace within bracket 0 comma  2 star pi # returns 50 points between 0 and 2pi

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| 02:37
| Hence, the default for the third argument is 50.

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| 02:42
| Let's now define a simple function that uses default arguments. 

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| 02:46
| We define a simple function that prints a welcome message to a person, given a greeting and his/her name.

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|02:54
|So type in the terminal def welcome within bracket greet comma  name= within double quotes World colon (hit enter)
                         print greet comma  name (hit enter)

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| 03:18
| Let us first call the function with two arguments, one for  greet  and other for  name .

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|03:25
|So type welcome  and in bracket  within double quotes Hi comma   within double quotes Guido

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| 03:35
| We get the expected welcome message, "Hi Guido".

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| 03:41
| Now let us call the function with just one argument "Hello".

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|03:45
|So type welcome within bracket  within double quotes Hello

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| 03:53
| "Hello" is treated as the greet  and we get "Hello World" as the output. 

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| 03:59
| "World" is the default value for the argument  name .

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| 04:02
| Pause the video here,  try out the following exercise and resume the video.

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| 04:07
| '''Redefine the function  welcome , by interchanging it's''' arguments. 

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| 04:11
| Place the name  argument with it's default value of "World" before the  greet  argument.

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|04:17
| Switch to the terminal for solution

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|04:20
|def welcome within bracket name= within double quotes World comma  greet colon (hit enter)
    print greet comma  name (hit enter)

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| 04:36
| We get an error that reads SyntaxError: non-default argument follows default argument .Then ipython control line one.

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| 04:47
| When defining a function all the argument with default values should come at the end.

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| 04:52
| Pause the video here, try out the following exercise and resume the video.

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| 04:58
| '''See the definition of linspace using  question mark  and make a note of all''' the arguments with default values are towards the end.

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| 05:09
| Switch to the terminal for solution

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|05:12
|linspace question mark hit enter

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| 05:17
| As we go on hitting the enter key, we the the number of arguments this command has. 

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| 05:26
| Please read the content on your terminal.  

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| 05:30
| Again,Pause the video here,try out the following exercise and resume the video.

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| 05:35
| '''Redefine the function  welcome  with a default value of'''

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| 05:41
| "Hello" to the  greet  argument. 

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| 05:44
| Then, call the function without any arguments.

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| 05:48
| Switch to the terminal for solution

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|05:51
|Type def welcome within bracket greet= within double quotes Hello comma  name= in double quotes World colon
    print greet comma  name
(After hitting enter type)
    welcome()

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| 06:17
| As we can see, we get the output as  Hello World .

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| 06:20
| Let us now learn what keyword arguments or named arguments are.

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| 06:26
| We shall refer to them as keyword arguments, henceforth.

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| 06:31
| When you are calling functions in Python, you don't need to remember the order in which to pass the arguments. 

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| 06:38
| Instead, you need the name of the argument to pass it a value. 

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| 06:44
| This slide shows a few function calls that use keyword arguments. 

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| 06:52
| loc , linewidth ,  xy  and  labels<  are being called with keyword arguments.

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| 07:00
| Let us try and understand this better using the  welcome  function that we have been using all along. 

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| 07:07
| Let us call it in different ways and observe the output to see how keyword arguments work.

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|07:14
|So type in terminal type welcome()

welcome within bracket  within double quotes Hello comma  double quotes James

welcome within bracket  within double quotes Hi comma  name= within double quotes Guido

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| 07:37
| When no keyword is specified, the arguments are allotted based on their position. 

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| 07:42
| So, "Hi" is the value of the argument greet  and name is passed the value "Guido".

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| 07:48
| If we type on the terminal welcome within bracket name= within double quotes Guido comma  greet= within double quotes Hey exclamation 

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|08:02
| When keyword arguments are used, the arguments can be called in any order. 

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| 08:07
| And if we call our function as,welcome within bracket name="Guido" comma  "Hey" 

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| 08:17
| This call returns an error that reads, non-keyword arg after keyword arg . Python expects all the keyword to be present towards the end.

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| 08:30
| That brings us to the end of what we wanted to learn about  keyword  arguments.

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| 08:37
| Before defining a function of your own, make sure that you check the standard library, for a similar function. 

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| 08:43
| Python is popularly called a "Batteries included" language, for the huge library that comes along with it.

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| 08:55
| Math functions - abs, sin, .... Plot functions - plot, bar, pie ... Boolean functions - and, or, not ...

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| 09:11
| Apart from the standard library there are other libraries like  pylab ,  scipy , etc which have a huge collection of functions for scientific purposes.

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| 09:22
| '''pylab''' has

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| 09:23
| plot, bar, contour, boxplot, errorbar, log, polar, quiver, semilog

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| 09:32
| '''scipy (modules)'''has

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| 09:35
| fftpack, stats, linalg, ndimage, signal, optimize, integrate

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|09:46
| This brings us to the end of this tutorial. 

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| 09:48
| In this tutorial, we have learnt to, 1. Define functions with default arguments.

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| 09:53
| 2. Call functions using keyword arguments.

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| 09:55
| 3. Use the range of functions available in the Python standard library and the Scientific Computing related packages.

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| 10:04
| Here are some self assessment questions for you to solve

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| 10:08
| 1. All arguments of a function cannot have default values. - True or False?

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| 10:14
| 2. The following is a valid function definition. 

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| 10:17
| True or False?

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| 10:21
|  def separator within bracket count=40 comma  char comma  show=False colon
  if show colon
  print char  star  count
  return char  star  count

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| 10:36
| 3. When calling a function, the arguments should always be in the order in which they are defined.

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| 10:45
|  the arguments can be in any order.

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| 10:47
|  '''only keyword arguments can be in any order, but should be called''' at the beginning.

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| 10:56
|  only keyword arguments can be in any order, and should be called at the end.

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| 11:10
| So now we can look at the answers,

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| 11:13
| 1.False. 

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| 11:15
| All arguments of a Python function can have default values.

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| 11:21
| 2. False. 

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| 11:23
| All parameters with default arguments should be defined at the end.

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| 11:27
| 3. When calling a function,only keyword arguments can be in any order, but should be called at the end.

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| 11:35
| Hope you have enjoyed this tutorial and found it useful. 

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| 11:39
| Thank you!

|}