1
00:00:00,000 --> 00:00:04,500
Strings are what are called an iterable, and they are a sequence,

2
00:00:04,500 --> 00:00:08,400
meaning that we can break them apart, and we can take action

3
00:00:08,410 --> 00:00:10,050
based on every single letter in a string.

4
00:00:10,220 --> 00:00:14,780
So with that comes this idea of an index, and we can do this

5
00:00:14,790 --> 00:00:17,780
with a list or an array or a tuple as well.

6
00:00:18,080 --> 00:00:22,490
So let's go ahead and make a string.

7
00:00:22,500 --> 00:00:28,100
So the 'course = "Python for Everybody".

8
00:00:28,300 --> 00:00:31,750
And an index is literally just a number.

9
00:00:31,760 --> 00:00:34,810
So it's your variable name, and then it's got the hard brackets,

10
00:00:35,020 --> 00:00:37,030
and then you just put a number in there.

11
00:00:37,040 --> 00:00:40,180
So number 0, because computers always start counting at

12
00:00:40,180 --> 00:00:43,800
0, is going to be the 'P', and then we can just simply count from there. So

13
00:00:43,890 --> 00:00:49,950
if we go 0-1-2-3-4-5, the fifth letter in here, the fifth

14
00:00:49,960 --> 00:00:53,080
number rather is going to be the 'n'.

15
00:00:53,620 --> 00:00:55,810
So let's go ahead and test out these assumptions.

16
00:00:55,940 --> 00:01:00,620
So index 0, again, that's just with your variable name,

17
00:01:00,630 --> 00:01:05,019
hard bracket, then your index number, and then closing hard

18
00:01:05,030 --> 00:01:08,230
bracket. 'P', just as expected.

19
00:01:08,240 --> 00:01:13,200
And 'course[]', what I say it was? 5, I believe, is going to

20
00:01:13,210 --> 00:01:15,480
be 'n', just like that.

21
00:01:15,490 --> 00:01:19,080
So in most programming languages an index tends to start

22
00:01:19,090 --> 00:01:22,290
with the number 0, not all of them, but most of them.

23
00:01:22,400 --> 00:01:27,500
So to humans, 0 really just doesn't mean anything.

24
00:01:27,510 --> 00:01:30,770
0 actually means literally nothing.

25
00:01:30,780 --> 00:01:32,720
And it's kind of crazy to think about,

26
00:01:32,730 --> 00:01:35,260
but to a computer, 0 is a number.

27
00:01:35,270 --> 00:01:39,010
So if I said you have 5 apples and I have 0 apples,

28
00:01:39,180 --> 00:01:40,530
well, I have nothing.

29
00:01:40,540 --> 00:01:42,570
I have a basket of nothing.

30
00:01:42,580 --> 00:01:44,370
It's just an empty basket of nothing.

31
00:01:44,380 --> 00:01:46,260
You might have a basket of apples.

32
00:01:46,270 --> 00:01:52,270
I have a basket of zero apples, aka a blank or empty or void

33
00:01:52,270 --> 00:01:57,400
basket. But to a computer, there is always that 0 number,

34
00:01:57,400 --> 00:02:01,100
and that's why computer languages usually start an index with the number

35
00:02:01,190 --> 00:02:04,260
0, it's because it's actually, it's a real thing for a computer.

36
00:02:04,270 --> 00:02:06,750
So that is indexing through a string.

37
00:02:06,800 --> 00:02:11,000
If we want to index through a list, we could do 'lst', short for list

38
00:02:11,000 --> 00:02:16,100
Because if I do 'list', you can see it sort of glows green a little bit,

39
00:02:16,140 --> 00:02:17,420
that is syntax highlighting.

40
00:02:17,420 --> 00:02:19,100
That means it's a reserved keyword.

41
00:02:19,100 --> 00:02:29,300
So let's just do 'lst = ['Car', 'Truck', 'Airplane', 'Blimp']'

42
00:02:29,320 --> 00:02:31,740
I don't know why I'm using any of these in this example,

43
00:02:31,950 --> 00:02:33,570
but let's take a look at this anyways.

44
00:02:33,780 --> 00:02:37,050
So I have this variable called 'lst' short for list.

45
00:02:37,200 --> 00:02:41,800
And if this follows the exact same pattern as up here, 'Car'

46
00:02:41,800 --> 00:02:44,500
will be 0, 'Truck' will be 1, 'Airplane' will be 2, and

47
00:02:44,580 --> 00:02:45,770
'Blimp' will be 3.

48
00:02:46,060 --> 00:02:48,400
And we can actually test out our assumptions here.

49
00:02:48,400 --> 00:02:50,900
So we can do 'list', index 0, 'list[0]'

50
00:02:50,900 --> 00:02:54,900
And that's not going to work because I actually typed 'list',

51
00:02:54,900 --> 00:02:57,900
it should be 'lst[0]', and there we go,

52
00:02:57,950 --> 00:03:00,880
we got 'Car'. 'lst[2]'.

53
00:03:02,000 --> 00:03:06,010
Just take a sec, and think about this one. Which one is going to be 2?

54
00:03:06,100 --> 00:03:08,300
[no audio]

55
00:03:08,320 --> 00:03:12,590
If you are thinking that index 2 is going to be 'Airplane',

56
00:03:12,590 --> 00:03:13,640
you're absolutely correct.

57
00:03:13,760 --> 00:03:16,370
If you think index 2 is going to be 'Truck', well remember

58
00:03:16,380 --> 00:03:18,530
we start counting at 0, 0-1-2.

59
00:03:18,860 --> 00:03:22,280
And if you've made that sort of mistake already, that is

60
00:03:22,280 --> 00:03:25,610
okay, because I've been doing this for 20 years and indexing

61
00:03:25,620 --> 00:03:28,610
still occasionally it still comes out and bites me as well.

62
00:03:28,620 --> 00:03:31,280
So it's just something to sort of wrap your head around.

63
00:03:31,290 --> 00:03:34,190
But we can see that 'lst[2]' is 'Airplane'.

64
00:03:34,300 --> 00:03:37,800
Now, just for funsies, let's go ahead and see if we can get the reverse.

65
00:03:38,060 --> 00:03:40,160
So let's do list with a negative number.

66
00:03:40,360 --> 00:03:42,760
Which one do you think this is going to provide

67
00:03:43,300 --> 00:03:47,650
if we start counting backwards from 0? This one is 'Blimp'.

68
00:03:48,800 --> 00:03:52,000
negative one, negative 2, negative three, negative 4.

69
00:03:52,500 --> 00:03:54,200
Let's try that again.

70
00:03:54,200 --> 00:03:56,600
'lst[-3]'.

71
00:03:56,600 --> 00:04:01,100
And if this holds up, -1, -2, -3, should be 'Truck'.

72
00:04:02,400 --> 00:04:03,600
And there we go.

73
00:04:03,650 --> 00:04:06,430
So now we have indexing forwards and backwards.

74
00:04:06,440 --> 00:04:08,890
Now that's just part of indexing.

75
00:04:08,900 --> 00:04:11,290
The other part of indexing is this thing called slicing.

76
00:04:11,480 --> 00:04:16,640
So if I type out the word 'course' here, we have "Python for

77
00:04:16,649 --> 00:04:19,709
Everybody". In a string we can slice very easily.

78
00:04:19,720 --> 00:04:23,440
All we have to do is say, 'course', where do we want to

79
00:04:23,440 --> 00:04:25,399
start? Let's start at the very beginning. That's the 'P'.

80
00:04:25,459 --> 00:04:28,630
And for how long do we want to go for, or up until rather?

81
00:04:28,660 --> 00:04:31,610
And let's say we want to go up until the number 5.

82
00:04:31,610 --> 00:04:36,300
So 0-1-2-3-4-5.

83
00:04:36,300 --> 00:04:37,600
Let's take a look at this.

84
00:04:37,600 --> 00:04:41,010
Well, this one only gives us "Pytho", not "Python".

85
00:04:41,220 --> 00:04:45,070
So if we wanted the whole word, we would have to use 'course

86
00:04:46,210 --> 00:04:47,080
[0:6]',

87
00:04:47,110 --> 00:04:48,820
and that will give us the word "Python".

88
00:04:49,060 --> 00:04:53,180
But let's also, let's slice the word 'for' out of here.

89
00:04:53,190 --> 00:04:57,400
So we've got 0-1-2-3-4-5-6.

90
00:04:57,410 --> 00:05:01,810
So we have to start on index 7, 8-9-10.

91
00:05:01,810 --> 00:05:05,300
So let's do 'course[7:10]'

92
00:05:05,300 --> 00:05:06,370
Let's see what this gives us.

93
00:05:06,420 --> 00:05:10,770
Gives us the word 'for', and that's slicing a string.

94
00:05:10,800 --> 00:05:12,420
Now we also have that 'lst', right,

95
00:05:12,430 --> 00:05:13,830
and we can slice a list as well.

96
00:05:13,900 --> 00:05:16,100
So let's slice this list. Let's do 'lst',

97
00:05:16,780 --> 00:05:20,820
let's grab number 1 and go up until number 3, 'lst[1:3]

98
00:05:20,820 --> 00:05:26,100
So 0-1-2-3, we're going to start at 1, 0-1.

99
00:05:26,100 --> 00:05:27,100
We're going to start at 'Truck',

100
00:05:27,100 --> 00:05:28,700
we're going to grab 'Airplane' as well,

101
00:05:28,740 --> 00:05:31,010
and we're going to go up to the third index.

102
00:05:31,010 --> 00:05:33,440
So we're not going to get 'Blimp', but we're just going to

103
00:05:33,700 --> 00:05:35,440
get up until 'Blimp'.

104
00:05:35,450 --> 00:05:37,780
So 'Truck' and 'Airplane' is what we should be getting back.

105
00:05:37,860 --> 00:05:39,840
And sure enough, there we go.

106
00:05:39,840 --> 00:05:45,900
We have now indexed and sliced a string and a list, so sequences.

107
00:05:45,900 --> 00:05:50,470
Last but not least, we can also take these slices or

108
00:05:50,480 --> 00:05:54,100
any of these indexes, and we can put them into another variable.

109
00:05:54,110 --> 00:05:55,900
So we have this variable called 'course',

110
00:05:55,910 --> 00:05:58,150
but what if we wanted to get a variable called 'language'?

111
00:05:59,100 --> 00:05:59,800
'language = course[,

112
00:05:59,820 --> 00:06:01,410
start at 0,

113
00:06:01,600 --> 00:06:02,600
go to six,

114
00:06:03,000 --> 00:06:04,100
hit 'Enter',

115
00:06:04,100 --> 00:06:06,100
[no audio]

116
00:06:06,100 --> 00:06:07,600
and there we go.

117
00:06:07,600 --> 00:06:09,700
We have 'language' as "Python",

118
00:06:09,700 --> 00:06:12,810
and 'course' is still "Python for Everybody".

119
00:06:12,840 --> 00:06:16,080
So all it did there was it took out this little piece of text,

120
00:06:16,260 --> 00:06:18,840
and threw it into a new variable called 'language'.

121
00:06:19,120 --> 00:06:24,460
Now, in most Python cases, at least Python cases I run into

122
00:06:24,500 --> 00:06:30,400
you won't use this one too often, but you will use list slicing quite a bit.

123
00:06:30,420 --> 00:06:35,220
So even though slicing or indexing a particular string or

124
00:06:35,230 --> 00:06:38,430
a sentence, well it's not actually super useful, it is good to

125
00:06:38,440 --> 00:06:40,230
know because you can also apply it to lists,

126
00:06:40,230 --> 00:06:42,700
you can apply it to tuples and things like that.