Difference between revisions of "Python/C4/Advanced-features-of-functions/English-timed"
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Latest revision as of 12:48, 27 March 2017
| Time | Narration |
| 00:01 | Hello friends and Welcome to the tutorial on 'advanced features of functions'. |
| 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". |
| 00:32 | Let us Start the ipython interpreter in command |
| 00:36 | ipython hypen pylab in command |
| 00:43 | Let's use the round function as an example to understand what a default value of an argument means. |
| 00:49 | Let's type the following expressions in the terminal. |
| 00:52 | Type round within bracket 2.484 and hit enter.Then type round 2.484 comma 2 |
| 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. |
| 01:22 | By observing the output, we can guess that the first one is equivalent to call with the second argument being 0. 0 . |
| 01:30 | s.strip() # strips on spaces. |
| 01:35 | s.strip within single quote at the rate # strips the string of 'at the rate' symbols. |
| 01:47 | Thus it can be said that here, blank space is the default argument. |
| 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. |
| 02:14 | Hence, here when third argument is not provided, it shows default line style. |
| 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 |
| 02:37 | Hence, the default for the third argument is 50. |
| 02:42 | Let's now define a simple function that uses default arguments. |
| 02:46 | We define a simple function that prints a welcome message to a person, given a greeting and his/her name. |
| 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) |
| 03:18 | Let us first call the function with two arguments, one for greet and other for name . |
| 03:25 | So type welcome and in bracket within double quotes Hi comma within double quotes Guido |
| 03:35 | We get the expected welcome message, "Hi Guido". |
| 03:41 | Now let us call the function with just one argument "Hello". |
| 03:45 | So type welcome within bracket within double quotes Hello |
| 03:53 | "Hello" is treated as the greet and we get "Hello World" as the output. |
| 03:59 | "World" is the default value for the argument name . |
| 04:02 | Pause the video here, try out the following exercise and resume the video. |
| 04:07 | Redefine the function welcome , by interchanging it's arguments. |
| 04:11 | Place the name argument with it's default value of "World" before the greet argument. |
| 04:17 | Switch to the terminal for solution |
| 04:20 | def welcome within bracket name= within double quotes World comma greet colon (hit enter), print greet comma name (hit enter) |
| 04:36 | We get an error that reads SyntaxError: non-default argument follows default argument .Then ipython control line one. |
| 04:47 | When defining a function all the argument with default values should come at the end. |
| 04:52 | Pause the video here, try out the following exercise and resume the video. |
| 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. |
| 05:09 | Switch to the terminal for solution |
| 05:12 | linspace question mark hit enter |
| 05:17 | As we go on hitting the enter key, we the the number of arguments this command has. |
| 05:26 | Please read the content on your terminal. |
| 05:30 | Again,Pause the video here,try out the following exercise and resume the video. |
| 05:35 | Redefine the function welcome with a default value of |
| 05:41 | "Hello" to the greet argument. |
| 05:44 | Then, call the function without any arguments. |
| 05:48 | Switch to the terminal for solution |
| 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() |
| 06:17 | As we can see, we get the output as Hello World . |
| 06:20 | Let us now learn what keyword arguments or named arguments are. |
| 06:26 | We shall refer to them as keyword arguments, henceforth. |
| 06:31 | When you are calling functions in Python, you don't need to remember the order in which to pass the arguments. |
| 06:38 | Instead, you need the name of the argument to pass it a value. |
| 06:44 | This slide shows a few function calls that use keyword arguments. |
| 06:52 | loc , linewidth , xy and labels< are being called with keyword arguments. |
| 07:00 | Let us try and understand this better using the welcome function that we have been using all along. |
| 07:07 | Let us call it in different ways and observe the output to see how keyword arguments work. |
| 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 |
| 07:37 | When no keyword is specified, the arguments are allotted based on their position. |
| 07:42 | So, "Hi" is the value of the argument greet and name is passed the value "Guido". |
| 07:48 | If we type on the terminal welcome within bracket name= within double quotes Guido comma greet= within double quotes Hey exclamation |
| 08:02 | When keyword arguments are used, the arguments can be called in any order. |
| 08:07 | And if we call our function as,welcome within bracket name="Guido" comma "Hey" |
| 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. |
| 08:30 | That brings us to the end of what we wanted to learn about keyword arguments. |
| 08:37 | Before defining a function of your own, make sure that you check the standard library, for a similar function. |
| 08:43 | Python is popularly called a "Batteries included" language, for the huge library that comes along with it. |
| 08:55 | Math functions - abs, sin, .... Plot functions - plot, bar, pie ... Boolean functions - and, or, not ... |
| 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. |
| 09:22 | pylab has plot, bar, contour, boxplot, errorbar, log, polar, quiver, semilog |
| 09:32 | scipy (modules)has |
| 09:35 | fftpack, stats, linalg, ndimage, signal, optimize, integrate |
| 09:46 | This brings us to the end of this tutorial. |
| 09:48 | In this tutorial, we have learnt to, 1. Define functions with default arguments. |
| 09:53 | Call functions using keyword arguments. |
| 09:55 | Use the range of functions available in the Python standard library and the Scientific Computing related packages. |
| 10:04 | Here are some self assessment questions for you to solve |
| 10:08 | All arguments of a function cannot have default values. - True or False? |
| 10:14 | The following is a valid function definition. |
| 10:17 | True or False? |
| 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 |
| 10:36 | When calling a function, the arguments should always be in the order in which they are defined. |
| 10:45 | the arguments can be in any order. |
| 10:47 | only keyword arguments can be in any order, but should be called at the beginning. |
| 10:56 | only keyword arguments can be in any order, and should be called at the end. |
| 11:10 | So now we can look at the answers, |
| 11:13 | False. |
| 11:15 | All arguments of a Python function can have default values. |
| 11:21 | False. |
| 11:23 | All parameters with default arguments should be defined at the end. |
| 11:27 | When calling a function,only keyword arguments can be in any order, but should be called at the end. |
| 11:35 | Hope you have enjoyed this tutorial and found it useful. |
| 11:39 | Thank you! |
