PoojaMoolya: Created page with "{| border=1 | '''Time''' | '''Narration''' |- | 00:01 | Welcome to the spoken tutorial on '''Manipulating Lists'''. |- | 00:06 | In th..."

2019-06-04T06:22:30Z

Created page with "{| border=1 | <center>'''Time'''</center> | <center>'''Narration'''</center> |- | 00:01 | Welcome to the spoken tutorial on '''Manipulating Lists'''. |- | 00:06 | In th..."

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{| border=1
| <center>'''Time'''</center>
| <center>'''Narration'''</center>

|-
| 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.

|}

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

PoojaMoolya: Created page with "{| border=1 | '''Time''' | '''Narration''' |- | 00:01 | Welcome to the spoken tutorial on '''Manipulating Lists'''. |- | 00:06 | In th..."