1
00:00:01,080 --> 00:00:02,240
Welcome back.

2
00:00:02,250 --> 00:00:07,710
Let's talk about some useful tricks with lists that you'll see a lot in Python code.

3
00:00:08,340 --> 00:00:12,130
Well one we have already seen it's this idea of length.

4
00:00:12,180 --> 00:00:19,320
You're going to be using this a lot that is to figure out the length of a list which in our case is

5
00:00:19,320 --> 00:00:20,980
now seven.

6
00:00:21,000 --> 00:00:25,920
Another really useful trick is to reverse a list.

7
00:00:25,920 --> 00:00:33,990
Now I've already showed you how to reverse a list but sometimes you can do that with list slicing against

8
00:00:33,990 --> 00:00:35,850
something that we've seen in String slicing.

9
00:00:36,090 --> 00:00:47,220
So I can actually do basket and then semicolon semicolon negative one if I click run here.

10
00:00:47,270 --> 00:00:57,110
Is that what you expected let's go through this line by line I've sorted the basket so that it's from

11
00:00:57,140 --> 00:01:00,950
a all the way to Z and then I've reversed this.

12
00:01:00,950 --> 00:01:03,740
So it's an Z all the way to a.

13
00:01:03,920 --> 00:01:11,370
And then I've reversed the basket again so that instead of being in reverse it's now in order.

14
00:01:11,390 --> 00:01:22,430
ABC D E X and this list slicing creates a new list right.

15
00:01:22,480 --> 00:01:32,570
If I print basket here you'll see that the basket is the reversed version.

16
00:01:32,570 --> 00:01:39,900
The last action that we've taken on it versus list slicing that creates a new version.

17
00:01:40,730 --> 00:01:45,810
So this notation you'll see a lot with lists when you need to reverse the list.

18
00:01:45,860 --> 00:01:53,220
Or maybe you need to make a copy of the list like this or maybe you need a portion of the list.

19
00:01:53,300 --> 00:02:01,420
Another useful thing that you'll see a lot of is something called range let's comment this out for now.

20
00:02:01,610 --> 00:02:08,060
If I wanted to generate a list really quickly let's say from 1 to 100 I can do something like this.

21
00:02:08,720 --> 00:02:13,970
I can say range and then start and then stop.

22
00:02:13,970 --> 00:02:19,510
So let's do a hundred and if I print this

23
00:02:23,260 --> 00:02:33,730
and I run I get a range 1 to 100 but if I wrap this in a list which is going to create a new list for

24
00:02:33,730 --> 00:02:40,260
us and I click Run look at that I get a range from 1 all the way to ninety nine.

25
00:02:40,280 --> 00:02:43,720
Remember it's the start and then whatever to stop it.

26
00:02:43,760 --> 00:02:46,440
So before it hits 100 it's going to stop.

27
00:02:46,670 --> 00:02:55,820
Now if I remove this and just do one single thing I get a list starting from zero all the way to ninety

28
00:02:55,820 --> 00:02:56,230
nine.

29
00:02:56,500 --> 00:03:03,490
If I want a list that has a hundred and one items because it starts at zero I would just do one hundred

30
00:03:03,550 --> 00:03:11,560
and one end range is something we'll talk about a lot more especially when we talk about loops in programming

31
00:03:12,490 --> 00:03:19,680
but this is a great way of you to generate a list really really quickly especially a numbered list.

32
00:03:19,690 --> 00:03:29,440
Finally the last common thing that you'll see a lot is this idea of DOT join what is dot join join is

33
00:03:29,440 --> 00:03:36,680
actually something that works on strings it's a string method but it's often used this way.

34
00:03:36,820 --> 00:03:42,580
We have an empty string and this empty string.

35
00:03:42,580 --> 00:03:47,040
Let's say sentence and then we can do a sentence.

36
00:03:47,040 --> 00:03:56,250
Dot join and join takes what we call an automobile which is a list for now.

37
00:03:56,250 --> 00:04:06,860
And in here we can have a sentence like high My name is

38
00:04:11,440 --> 00:04:17,060
and now if I print sentence and I click run here.

39
00:04:17,090 --> 00:04:17,390
Hmm.

40
00:04:17,780 --> 00:04:19,620
I don't get anything.

41
00:04:19,760 --> 00:04:21,420
Let's figure out why.

42
00:04:21,470 --> 00:04:27,520
What if I type in an exclamation mark here and I click Run All right.

43
00:04:27,520 --> 00:04:33,310
It's printing out sentence but it looks like Doug join creates a new item for us.

44
00:04:33,310 --> 00:04:40,990
So let's just sign that to the new sentence.

45
00:04:41,150 --> 00:04:45,290
Now if I do new sentence and print that out

46
00:04:48,390 --> 00:04:54,700
we see that I get Hi my name is Jo Jo.

47
00:04:54,840 --> 00:04:57,710
So this is a little funky right.

48
00:04:57,710 --> 00:05:06,620
We have these exclamation marks between our items and join joins these little interval items.

49
00:05:06,630 --> 00:05:10,070
These lists by whatever is in front of it.

50
00:05:10,230 --> 00:05:17,300
So if we actually change this to an empty string click Run we now get this.

51
00:05:17,340 --> 00:05:21,540
If I add a space in between and click Run we get.

52
00:05:21,550 --> 00:05:29,150
Hi my name is Jojo and sometimes you'll notice this pattern a lot especially if you want to join and

53
00:05:29,150 --> 00:05:33,270
create a new string out of a list of items.

54
00:05:33,320 --> 00:05:40,460
Now a shorthand way of doing this is to actually not even bother with this and just doing an empty string

55
00:05:41,970 --> 00:05:47,760
dot joint and then joining all the list items.

56
00:05:47,790 --> 00:05:48,930
There we go.

57
00:05:48,930 --> 00:05:52,090
So all we're doing is combining lists into a strength.

58
00:05:52,110 --> 00:05:56,800
And this is a common pattern that you'll see a lot of I'll see in the next one by.