Python-3.4.3/C4/Advanced-Features-of-Functions/English-timed

Time	Narration
00:01	Welcome to the spoken tutorial on Advanced Features of Functions.
00:07	In this tutorial, we will learn to- Assign default values to arguments, when defining functions
00:15	Define and call functions with keyword arguments
00:20	Define and call functions with arbitrary arguments
00:25	Learn some of the built-in functions available in Python standard library.
00:31	To record this tutorial, I am using Ubuntu Linux 16.04 operating system
00:38	Python 3.4.3 and IPython 5.1.0
00:45	To practise this tutorial, you should know how to run basic Python commands on the IPython console use functions.
00:55	If not, see the relevant Python tutorials on this website.
01:00	First let us see about default arguments in Python.
01:05	Function arguments can have default values in Python.
01:10	When we call a function without a value for an argument, its default value is used if available
01:18	Otherwise it will give error.
01:21	Let us start ipython. Open the terminal.
01:26	Type ipython3 and press Enter.
01:30	From here onwards, remember to press the Enter key after typing every command on the terminal.
01:37	Let us define a function Welcome.
01:40	Type the code as shown.
01:44	Here, welcome is the function name greet is the argument with no default values and the name argument has a default value World.
01:55	In a function, all the arguments with default values should come after non-default arguments.
02:03	Let us first call the function welcome with two arguments
02:08	Type, welcome inside brackets inside double quotes Hi comma inside double quotes Chandru
02:17	We get the expected welcome message, Hi Chandru.
02:21	Now let us call the function with one argument only.
02:25	Type, welcome inside brackets inside double quotes Hello
02:31	We get the output as Hello World.
02:35	Here, “Hello” is passed to the parameter greet and
02:39	“World” is the default value of the name parameter.
02:44	Let us add another parameter age with default value as 23 as shown.
02:51	Now type, welcome inside brackets inside double quotes Hello
02:58	Here, welcome function still works since we have provided default value for age.
03:06	Default values allow us to add new parameters to an existing function.
03:12	It will not break the existing usage of the function.
03:16	Pause the video. Try this exercise and then resume the video.
03:22	Redefine the function welcome, by interchanging its arguments.
03:27	Place the name argument with its default value of "World" before the greet argument.
03:34	Switch to the terminal for the solution.
03:38	Type as shown.
03:42	We get an error that reads SyntaxError: non-default argument follows default argument.
03:50	When defining a function all the arguments with default values should come at the end.
03:57	Pause the video. Try this exercise and then resume the video.
04:03	Redefine the function welcome with a default value of "Hello" to the greet argument.
04:10	Then, call the function without any arguments.
04:14	Switch to the terminal for the solution.
04:18	Type as shown.
04:21	Then type, welcome open and close brackets
04:26	As we can see, we get the output as Hello World.
04:31	Default values of both parameters are used since function is called without passing any value.
04:39	Next let us see what are keyword arguments.
04:43	We no need to remember the order of arguments while calling functions by passing keyword arguments.
04:51	Instead, we can use name of the argument to pass a value to it.
04:57	Let us define a function with name marks which takes three marks as arguments.
05:04	Type as shown. Then we will call the marks function without specifying the keywords.
05:11	Type, marks inside brackets 34 comma 23 comma 45
05:18	We get the output as “first: 34 second: 23 and third: 45”
05:24	Here the values 34, 23 and 45 are passed according to the position.
05:31	To confirm this, we will try with different values.
05:35	Type, marks inside brackets 34 comma 45 comma 23
05:42	We can see that the printed values are changed since they are passed according to the position.
05:49	Now let us pass two values without keyword and other one with keyword.
05:55	Type, marks inside brackets 34 comma 23 comma third is equal to 45
06:04	Here first two values are passed according to the position and the third as keyword argument.
06:12	But, the keyword arguments should be specified at the end.
06:17	Now type, marks inside brackets 34 comma second is equal to 23 comma 45
06:26	We get the SyntaxError, positional argument follows keyword argument.
06:32	This is because here the keyword argument is not specified at the end.
06:38	We can pass all the parameters as keyword arguments.
06:43	Type, marks inside brackets second is equal to 34 comma first is equal to 23 comma third is equal to 45
06:54	Here even though the order of keyword is changed, we get the output as: “first: 23 second: 34 and third: 45”
07:03	Next we will learn to define a function to take only keyword arguments.
07:09	Type as shown.
07:12	Then to call the function, type, marks inside brackets second is equal to 34 comma first is equal to 23 comma third is equal to 45
07:25	Note the asterisk symbol at the starting of parameters.
07:29	It restricts the function to accept keyword only arguments.
07:34	Again we will try to call the function without keyword arguments.
07:39	Type, marks inside brackets 45 comma 34 comma 23
07:46	It gives a TypeError as marks() takes 0 positional arguments but 3 were given.
07:53	This way we can enforce usage of keyword only arguments without positional arguments.
08:00	Next let us learn to use arbitrary arguments.
08:05	We may not always know in advance the number of arguments that will be passed into a function.
08:12	Use an asterisk(*) before an argument name to denote arbitrary number of arguments.
08:19	We can define a function to accept any number of positional arguments.
08:25	Type as shown. Then type, family inside brackets inside double quotes Duryodhana comma inside double quotes Dushasana
08:38	Here, we have called the function with multiple arguments.
08:43	These arguments get wrapped up into a tuple while passed into the function.
08:49	Now type as shown.
08:53	As you can see, we can call the function family with more values passed to the names argument.
09:01	We have passed 2 values in the first call and 4 values in the second call to the function family.
09:09	In both cases these values are assigned to the parameter names.
09:15	We can also define a function to receive arbitrary number of keyword arguments.
09:21	Type as shown. Then to call the function type as shown.
09:29	The person function prints a dictionary of keyword arguments passed to it.
09:35	Note the double asterisk symbol at the beginning of the parameter names.
09:40	It enables to pass zero or more keyword arguments.
09:45	Note: Single asterisk (*) symbol is used to accept arbitrary number of positional arguments.
09:53	And the double asterisk (**) symbol is used to accept arbitrary number of keyword arguments.
10:01	Now call the person function as shown.
10:06	Here we have passed 3 keyword arguments in the first case and 4 in the second case.
10:14	The function prints a dictionary of keyword arguments with values.
10:20	Python also provides built-in functions.
10:22	Some are abs() any()
10:29	dir() help()
10:33	You can visit this link to get the full list of built-in functions and their usage.
10:39	This brings us to the end of this tutorial. Let us summarize.
10:45	In this tutorial, we have learned to define functions with, Default arguments, keyword arguments and Arbitrary arguments
10:55	Here are some self assessment questions for you to solve.
11:00	All the arguments of a function cannot have default values. - True or False?
11:08	The following is a valid function definition. True or False?
11:15	While calling a function, which one is correct in the following.
11:20	And the answers, First. False. All the arguments of a Python function can have default values.
11:28	Second. False. All the parameters with default arguments should be defined at the end.
11:35	Third. While calling a function, only keyword arguments can be in any order, but should be called at the end.
11:44	Please post your timed queries in this forum.
11:48	Please post your general queries on Python in this forum.
11:53	FOSSEE team coordinates the TBC project.
11:57	Spoken Tutorial Project is funded by NMEICT, MHRD, Govt. of India. For more details, visit this website.
12:06	This is Priya from IIT Bombay signing off. Thanks for watching.

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