Python-3.4.3/C2/Getting-started-with-Lists/English

Python/C2/Getting Started with Lists/English

Title of script: Getting Started with Lists

Author: Aditya Palaparthy

Keywords: Python, IPython, list, del, remove, append

Visual Cue	Narration
Show Title Slide	Hello Friends. Welcome to the tutorial on "Getting started with lists".
Show Slide Objectives	At the end of this tutorial, you will be able to, Create lists Access list elements Append elements to lists Delete elements from lists
Show slide System Specifications	To record this tutorial, I am using Ubuntu Linux 14.04 operating system Python 3.4.3 IPython 5.1.0
Show Slide Pre-requisites	To practise this tutorial, you should know how to run basic Python commands on the ipython console If not, see the relevant Python tutorials on this website.
Show Slide List	What is a List? A List can store a sequence of elements. All elements need not be of the same data types
[Terminal] ipython3	Let us open the Terminal by pressing Ctrl+Alt+T keys simultaneously Now, type ipython3 and press Enter. We are now in the ipython prompt. Let us clear the terminal by pressing Ctrl + L for better view.
[IPython Terminal] mylist = ['spam', 'eggs', 100, 1.234] Highlight spam and eggs	Let us define a list with a variable name mylist Type mylist equal to inside square brackets inside quotes spam comma inside quotes eggs comma hundred comma one point two three four and press Enter. In Python, strings are always placed inside single or double quotes.
type(mylist) Highlight the command	Now enter type within brackets mylist and press Enter. Here type is a function which will return the datatype of the variable. mylist is a list datatype.
Highlight according to narration	As we can see, lists can contain elements of different datatypes In mylist, spam and eggs are strings, whereas hundred and one point two three four are integer and float respectively.
Show slide What is a variable? variable must either start with an alphabet or an underscore. They cannot start with numbers and cannot be the same as Python keywords.	In the code typed earlier, the name mylist is a variable. In Python, a variable must either start with an alphabet or an underscore. They cannot start with numbers and cannot be the same as Python keywords.
Examples of Keywords: for, if, else, elif, while, in, def, or, and A variable name cannot have spaces or punctuation characters or any arithmetic characters.	You will learn about keywords as we proceed. Few examples of keywords are “for, if, else, elif, while, in, def, or, and”. A variable name cannot have spaces or punctuation characters or any arithmetic characters.
show slide Valid and invalid variables Valid variable names: x, y, xx, abc, a_b_c, a1, variable1, mylist, _x foreign, spiff, while_true, or_else, and_od_else_1 Invalid names: 1_x, 2_var, x-, x+, x;, x: x y, x+y x*y x&^ae for, in, elif	These are some of the valid and invalid variable names.
Switch to the terminal Highlight mylist = ['spam', 'eggs', 100, 1.234]	Getting back to our lists, the list could be created as num underscore list is equal to inside square brackets '''one comma two' and press Enter or x equal to inside square brackets inside quotes a comma inside quotes b and press Enter Any valid variable name could be used.
[IPython Terminal] myemptylist = []	Let us now create an empty list with no elements. Type myemptylist is equal to open and close square brackets and press Enter. This is an empty list without any element
slide list index	We can access an element of a list using its corresponding index or position. Index value of the elements starts from 0, 1, 2 and so on. Negative indices are used to access elements from the end. Which starts from -1, -2, and so on The syntax to get a specific list element is variable inside square brackets elements index value
	Switch to the terminal.
[IPython Terminal] mylist[0] mylist[1] mylist[3]	Type mylist inside square brackets zero and press Enter. As we can see mylist[0] gives the first element spam Type mylist inside square brackets one and press Enter. mylist[1] gives the second element.
Show Slide Exercise1	Pause the video. Try this exercise and then resume the video. What happens when you type mylist[-1].
[IPython Terminal] mylist[-1]	Switch to the terminal for solution Type mylist inside square brackets minus one and press Enter. As you can see you get the last element which is one point two three four.
slide List in list	We can also create a list inside a list. This property makes lists heterogeneous data structures. This is the syntax for list inside a list.
[IPython Terminal] doublelist=[‘a’, [‘b’,’c’,’d’], 'and', 5, 6, 7, 8] Highlight [‘b’,’c’,’d’]	Let us include a list within a list for the variable doublelist. Type the code as shown here: Here b c d is a list in list which is represented within square brackets inside a list.
Type: doublelist[1] and press Enter	Now let us fetch some element from doublelist. Type: doublelist inside square brackets one and press Enter We can see the output as b c d within square brackets. This is because the index value one contains the list inside a list as its element.
Highlight according to narration	Now let us try to access a specific element, say b from the list inside a list. For this type: doublelist inside square brackets one inside square brackets zero and press Enter. Here the 1st parameter represents the index of the list in the main list. The second parameter represents the index value of b in the list inside the list.
Show Slide Exercise2	Pause the video. Try this exercise and then resume the video. doublelist=[‘a’, [‘b’,’c’,’d’], 'and', 5, 6, 7, 8] What is the command to get the element 'and' in the list doublelist? How would you get 'and' using negative indices? How would you get element 'd' from the list doublelist?
Show Slide Solution 2	The solution is on your screen.
slide len function len function is used to check the number of elements in the list. Syntax: len(variable)	We can use len function to check the number of elements/length of in the list. The syntax is: len inside parentheses variable
[IPython Terminal] len(mylist)	Let us find the number of elements in mylist which we created earlier. Switch to the terminal and clear the screen. Recall mylist by pressing up arrow key and press Enter. Type len inside parentheses mylist and press Enter. We get the length of mylist as four.
Slide Append function	We can append elements to the list using the append function. This function will add the element to the end of the list. The syntax is: variable dot append within parentheses element to be added.
[IPython Terminal] mylist.append('sharp') mylist.append(6)	Switch to the terminal Now type mylist dot append inside parentheses within quotes sharp and press Enter. Type mylist dot append inside parentheses six and press Enter. Let us check the updated mylist. Type mylist and press Enter We can see mylist is appended with sharp and six at the end.
slide del	We can also remove elements from lists. There are two ways of doing it. One is by using the index with del keyword. Syntax is del variable inside square brackets element’s index value.
slide remove	The other way is removing element by the value using remove function Syntax is variable dot remove inside parentheses element to be removed
mylist [IPython Terminal] del mylist[1] mylist	Switch to the terminal. Type mylist and press Enter to see the updated list. Type del space mylist inside square brackets one and press Enter. The keyword del deletes the element at index one, i.e the second element of the list, eggs. Again type mylist and press Enter. We can see that the element eggs has been deleted from the list.
[IPython Terminal] mylist.remove(100) mylist	Let us delete the element hundred from mylist list. For this we can use the function remove. Type mylist dot remove within parentheses hundred and press Enter. Let us check the updated mylist.
[IPython Terminal] mylist.append('spam') Highlight spam	What if the elements are repeated? To check that, let’s do a small experiment. Type mylist dot append within parentheses within quotes spam and press Enter Type mylist and press Enter Here is the updated mylist. It contains the element spam twice. One is at the start and the next is at the end of the list.
mylist.remove('spam') Type mylist	Now remove the element spam by typing: mylist dot remove inside parentheses inside quotes spam and press Enter. Let us check updated mylist.
Pause for a while	We can see that only the first occurrence of 'spam' has been removed. The function remove removes the first occurrence of the element in the sequence. Remember, the del keyword removes the element by index value. remove function removes on the basis of element being passed on.
	Using remove function, we can also remove an element with its index value. Let us try this with an example.
[Ipython Terminal] k = [1,2,1,3] k.remove(k[2]) k	Type k is equal to inside square brackets one comma two comma one comma three and press Enter Then type k dot remove inside parentheses k inside square brackets two and press Enter Type k and press Enter We can see the output as [2,1,3]. Since it deletes the first occurrence of what is returned by k inside square brackets two which is one.
Show Slide Exercise 3	Pause the video. Try this exercise and then resume the video. 1. Delete the fourth element from the list doublelist. 2. Remove 'and' from the list doublelist.
Show Slide Exercise 3	The solution is on your screen.
Show Slide Summary slide	This brings us to the end of this tutorial. In this tutorial, we have learnt to create: List with elements Empty list List within a list
	We also learnt to, Find out the list length using len function. Access elements using their index numbers. Append elements to list using the function append. Delete element from list using the del and remove function
Show Slide Evaluation	Here are some self assessment questions for you to solve How do you create an empty list? Can you have a list inside a list? How would you access the last element of a list without finding its length?
Show Slide Solutions	And the answers, We create an empty list just by leaving the space inside the square brackets empty. myemptylist equal to open and close square brackets. Yes, list can contain all the other data types, including list. Using negative indices, we can access the last element from the list.
Show Slide: Forum	Please post your timed queries in this forum.
Show Slide: Fossee Forum	Please post your general queries on Python in this forum.
Show Slide: Textbook Companion	FOSSEE team coordinates the TBC project.
Show Slide: Acknowledgement	Spoken-tutorial is funded by NMEICT, MHRD, Govt. of India. For more details, visit this website.
Show Slide Thank You	This is Trupti Kini from IIT Bombay signing off. Thank you.

Contributors and Content Editors

Nancyvarkey, Trupti