Python-3.4.3/C3/Manipulating-lists/English-timed

Time	Narration
00:01	Welcome to the spoken tutorial on Manipulating Lists.
00:06	In this tutorial, we will learn about slicing and striding of lists
00:12	Sort and reverse lists.
00:15	To record this tutorial, I am using Ubuntu Linux 16.04 operating system
00:23	Python 3.4.3 and IPython 5.1.0
00:30	To practise this tutorial, you should know how to run basic Python commands on the ipython console and use lists
00:41	If not, see the relevant Python tutorials on this website.
00:46	We have already learnt about list and how to access individual elements in the list.
00:53	Now we will see about slicing of lists.
00:57	The syntax for slicing is p inside square brackets start colon stop.
01:04	It returns all the elements of p between start and stop values.
01:11	The element with the stop index value will not be included.
01:16	Let us start ipython. Open the terminal.
01:21	Type ipython3 and press Enter.
01:27	From here onwards, remember to press the Enter key after typing every command on the terminal.
01:34	Let us understand the slicing with an example. Type, primes is equal to then type as shown.
01:45	Now we will try to obtain all the primes between 10 and 20 from the above list of primes.
01:52	Type, primes inside square brackets 4 colon 8
01:59	Recall that the start index value is 0.
02:03	Observe that the first element we want is 11 which has index 4 in the list. So, start value is 4.
02:12	Also, 19 is the last element we require which has index 7 in the list.
02:19	The element with index equal to stop value will not be included. So, end value is 8.
02:26	Pause the video. Try this exercise and then resume the video.
02:32	Obtain the primes less than 10, from the list primes.
02:37	Switch back to terminal for the solution
02:41	Type, primes inside square brackets 0 colon 4
02:47	Observe that in this case, our start value is 0.
02:52	7 is the last element we require which has index 3 in the list. So, the end value is 4.
03:01	Next we will learn to use step value in slicing.
03:06	Type 0 to 13 in a list and assign it to a variable num as shown.
03:13	Let us say, we want all the odd numbers less than 10 from the list num.
03:19	We will specify the step value in which the slice must be obtained.
03:25	Type num inside square brackets 1 colon 10 colon 2
03:31	We have to start from element with index 1 upto index 10 in steps of 2.
03:39	It is called striding of list. Press Enter to get the output.
03:45	We got the odd numbers less than 10.
03:48	When no step is specified, it is assumed to be 1.
03:53	Similarly, there are default values for start and stop as well.
03:59	Type, num inside square brackets colon 10
04:04	It gives the first 10 elements of the list.
04:08	If we don't specify the start value, the first element of the list is taken as starting.
04:15	Type, num inside square brackets 10 colon
04:21	This gives us all the elements from 10th element to the end.
04:26	If we don't specify the stop value, the elements till the last index of the list will be returned.
04:33	Start or end value can be negative to indicate that they are counted from the end of the list.
04:40	Next let us get all the even numbers in the list "num"
04:45	Observe that all the even numbers are at even index locations.
04:51	So, type num inside square brackets colon colon 2
04:58	We got all the even numbers. This is called striding.
05:04	Pause the video. Try this exercise and then resume the video.
05:10	Obtain all the multiples of three from the list num.
05:15	Switch back to terminal for the solution
05:19	Type, num inside square brackets colon colon 3
05:25	It gives us every third element from the list (i.e) multiples of 3.
05:31	Next let us learn to sort a list.
05:35	Type, a is equal to inside square brackets 5, 1, 6, 7, 7, 10
05:45	sort method is used to sort a list.
05:49	Type, a.sort open and close brackets
05:55	Type, a to get the output. We can see that the contents of the list a is sorted now.
06:04	Python provides a built-in function called sorted.
06:08	sorted function sorts the list which is passed as an argument to it.
06:14	It returns a new sorted list.
06:17	Again we will assign the same value to a as shown.
06:23	Type, sorted inside brackets a
06:28	We can store this sorted list into another list variable sa.
06:34	Type, sa is equal to sorted inside brackets a
06:41	To see the sorted list, type sa
06:46	Python also provides the reverse method which reverses the list in place.
06:52	Type, r is equal to inside square brackets 1 comma 2 comma 3 comma 4 comma 5
07:01	r dot reverse open and close brackets
07:06	To see the list r, type, r
07:10	We got the reverse of the list.
07:13	The original list r is changed now.
07:17	To reverse a list, we can also use striding with negative values.
07:22	Again we will assign the same value to r as shown.
07:27	Type, r inside square brackets colon colon minus 1
07:33	We can also store this new reversed list in another variable.
07:38	Type, ra is equal to r inside square brackets colon colon minus 1
07:46	To see the reversed list, type ra
07:51	Pause the video. Try this exercise and then resume the video.
07:57	Given below is the list of marks of a student in an examination. Obtain a list with marks in descending order.
08:06	Switch back to the terminal for the solution.
08:10	Type the list of marks as shown.
08:14	To get the marks in descending order type, sorted inside brackets marks inside square brackets colon colon minus 1
08:26	We can also get the same output by typing, sorted inside brackets marks comma reverse equal to True
08:38	This brings us to the end of this tutorial. Let us summarize.
08:44	In this tutorial, we have learnt to, Obtain the parts of lists using slicing and striding.
08:52	Sort lists using the sort method. Use the method reverse to reverse the lists.
09:00	Here are some self assessment questions for you to solve
09:05	First. Given the list primes. How do you obtain the last 4 prime numbers?
09:11	Second. Given a list p, of unknown length. Obtain the first 3 characters of it.
09:19	And the answers, First. The last four primes can be obtained from the given list as, primes inside square brackets minus 4 colon
09:30	Second. The first 3 characters can be obtained as, p inside square brackets colon 3
09:37	Please post your timed queries in this forum.
09:41	Please post your general queries on Python in this forum.
09:46	FOSSEE team coordinates the TBC project.
09:50	Spoken Tutorial Project is funded by NMEICT, MHRD, Govt. of India. For more details, visit this website.
10:01	This is Priya from IIT Bombay signing off. Thanks for watching.

Contributors and Content Editors

PoojaMoolya