Would you like to inspect the original subtitles? These are the user uploaded subtitles that are being translated: 1 00:00:00,030 --> 00:00:04,290 Hi again, in the previous lecture we talked about strings and in this lecture 3 00:00:04,290 --> 00:00:10,500 again we are going deeper into learning strings and specifically we're going to add 5 00:00:10,500 --> 00:00:16,260 indexing. Indexing is a very important concept not only with strings but 7 00:00:16,260 --> 00:00:21,150 with all the data type that we'll be looking at later such as lists, 9 00:00:21,150 --> 00:00:26,880 tuples and dictionaries, so please follow this lecture. Yeah, let's talk about 11 00:00:26,880 --> 00:00:35,070 indexing. Let me open the Python interactive session. Let me create a 13 00:00:35,070 --> 00:00:44,070 string, "Hi there!" exclamation mark and close quote. 15 00:00:44,070 --> 00:00:48,989 Now when you create a string, every string that you create Python under the hood 17 00:00:48,989 --> 00:00:57,930 what it does is it assigns a number to each or the items of your string so it 19 00:00:57,930 --> 00:01:06,780 starts from 0 so H will be assigned an index of 0 and then a 1 for I, 2 for the 21 00:01:06,780 --> 00:01:12,799 space, 3 for T, five, six seven, eight. 23 00:01:12,799 --> 00:01:18,990 So the exclamation mark character will will have an index of eight, so you would 25 00:01:18,990 --> 00:01:26,360 ask why is this useful? Well this allows you to extract certain parts from a 27 00:01:26,360 --> 00:01:33,600 string and there is a certain notation to do that you'd want to access the string. 29 00:01:33,600 --> 00:01:39,270 So in this case that's variable C holding the string, then you want to use 31 00:01:39,270 --> 00:01:44,579 square brackets so an opening square bracket and then a closing square 33 00:01:44,579 --> 00:01:49,350 bracket and inside those square brackets you pass the index of the item that you want 35 00:01:49,350 --> 00:01:58,170 to extract. Let's say I want the T character so that would be 0 1 2 3. 37 00:01:58,170 --> 00:02:05,490 I pass number 3 there as an index and that will extract for me the letter T which is 39 00:02:05,490 --> 00:02:10,800 actually a string. So you can check the type of the 41 00:02:10,800 --> 00:02:15,810 output and you'll see that that's a string, so a string is made of strings. 43 00:02:15,810 --> 00:02:22,950 You can say so. If you wanted H you'd past zero and if you wanted a lost 45 00:02:22,950 --> 00:02:28,260 character well you might have to count so one two three four five six seven 47 00:02:28,260 --> 00:02:33,330 eight. And so, and sorry including type there. 49 00:02:33,330 --> 00:02:38,880 Sorry about that! so c8 would give you the exclamation 51 00:02:38,880 --> 00:02:45,720 mark, but there's also another indexing system there that Python uses so in this 53 00:02:45,720 --> 00:02:50,519 case we had to count from the beginning to the end of the string but wouldn't it 55 00:02:50,519 --> 00:02:56,370 be useful if you had another system that lets you count from the end, so from 57 00:02:56,370 --> 00:03:00,780 right to left? Well, such a system exists and it 59 00:03:00,780 --> 00:03:08,400 starts from minus 1, so the exclamation mark would be minus 1 now that you can 61 00:03:08,400 --> 00:03:18,989 extract that with that. Minus 2 would be E, R would be minus 3 and so on up to H, so we 63 00:03:18,989 --> 00:03:25,019 have two indexing systems there which allow you to extract items depending on 65 00:03:25,019 --> 00:03:30,090 whether the items are in the beginning or near the end. Now what if you want to 67 00:03:30,090 --> 00:03:36,959 extract more than one item from a string? Let's say you want to extract Hi. 69 00:03:36,959 --> 00:03:47,090 Well there is a notation for that too, so Hi is expanding from index 0 to index 1. 71 00:03:47,090 --> 00:03:57,380 So up to here. So let's try 0 to 1. That will not work a very good, but let's see. 73 00:03:57,380 --> 00:04:05,130 So as I said this will return only H, so it doesn't return item with index 1. 75 00:04:05,130 --> 00:04:11,250 That's because splitting in Python, so we we're splitting a string here 77 00:04:11,250 --> 00:04:17,609 splitting in Python is upper bound exclusive, which means that the upper 79 00:04:17,609 --> 00:04:24,730 bounds of the split here is not included in the output and so if you want to 81 00:04:24,730 --> 00:04:33,070 include I you want to pass the index after I which is two so this is the string 83 00:04:33,070 --> 00:04:40,420 just for reference, so we extracted item with index 0 and item with index 1. 85 00:04:40,420 --> 00:04:46,770 And then the split starts right there at index 2 so it doesn't include the space. 87 00:04:46,770 --> 00:04:54,430 Just hi. If you pass 3 there, that would include the wide space as well and 89 00:04:54,430 --> 00:05:00,310 similarly you can pass like one. That will include the I and the space, there 91 00:05:00,310 --> 00:05:06,970 are also shortcuts, so if you pass zero like nothing to 3 but that is the same 93 00:05:06,970 --> 00:05:18,120 as doing 0 to 3 so it will include 0 1 & 2 and similarly if you want to extract 95 00:05:18,120 --> 00:05:24,760 there with the exclamation mark well what you'd want to do is T would 97 00:05:24,760 --> 00:05:32,919 have an index of 0 1 2 3 so 3 and then you can just pass a column there and 99 00:05:32,919 --> 00:05:38,830 execute it and that will give you There with the exclamation mark. Let's now try 101 00:05:38,830 --> 00:05:46,240 to extract R and E using negative indexing, so something to know is that 103 00:05:46,240 --> 00:05:50,200 even though we are using a negative indexing which starts from right to left 105 00:05:50,200 --> 00:05:56,530 the splitting will work from left to right which means the first index you 107 00:05:56,530 --> 00:06:05,140 want to pass is that of the first item. So R we pass minus 3 for R because 109 00:06:05,140 --> 00:06:15,300 you know we have minus 1, minus 2 and minus 3. So minus 3 for R and then we want E 111 00:06:15,300 --> 00:06:21,450 which is minus 2, but since splitting is upper bounce 113 00:06:21,450 --> 00:06:30,430 exclusive we want to pass minus one there. So let's try that, minus one, execute and yeah 115 00:06:30,430 --> 00:06:35,360 we get the correct output. That's the idea. If you didn't pass 117 00:06:35,360 --> 00:06:40,640 anything here you'd get the exclamation mark as well. So it will take a while 119 00:06:40,640 --> 00:06:45,050 until we get used to this, but with some practice you'll be able to remember 121 00:06:45,050 --> 00:06:52,010 these notations. Yeah, that's what I wanted to cover in this lecture, so this was 123 00:06:52,010 --> 00:06:58,100 about string indexing and splitting, so you split using the index that Python 125 00:06:58,100 --> 00:07:02,660 uses on the background. Yeah, I hope you enjoyed this and I'll talk to you 127 00:07:02,660 --> 00:07:05,470 later, thanks! 7544