1 00:00:04,420 --> 00:00:09,380 So far we've only been providing two values to our slices, the start and stop 2 00:00:09,380 --> 00:00:15,080 values. But slices can also take a step value, which defaults to one. So let's see 3 00:00:15,080 --> 00:00:19,189 some examples before we discuss the syntax more formally. So what I'm going 4 00:00:19,189 --> 00:00:23,400 to do is delete the code, other than the definition of parrot on line 3, 5 00:00:23,400 --> 00:00:29,810 and I'm going to type on line 5, print parenthesis parrot square bracket 6 00:00:29,810 --> 00:00:34,820 0:6:2, and close off the square bracket and parentheses, and we'll put a 7 00:00:34,820 --> 00:00:40,310 comment to the effect of the output being capital N r e. And on line 6 I'm 8 00:00:40,310 --> 00:00:45,770 going to type print parenthesis parrot left square bracket 0:6:3 this 9 00:00:45,770 --> 00:00:50,600 time, and right square bracket and parenthesis, and comment, the output 10 00:00:50,600 --> 00:00:56,570 should be Nw. So the slice on line 5 is starting from index 0, which is the 11 00:00:56,570 --> 00:01:01,730 capital N, extracting all the characters up to, but not including index 6, which is 12 00:01:01,730 --> 00:01:05,760 the i, in steps of 2. 13 00:01:33,720 --> 00:01:37,900 So let's confirm that that works by running it, and you 14 00:01:37,909 --> 00:01:41,270 can see we get the output that we thought we should get, and you can see 15 00:01:41,270 --> 00:01:45,500 that we've got that output. Alright so another example of a slice where the 16 00:01:45,500 --> 00:01:49,610 step is as follows; so I'm going to start type some code on line 8. I'm going to start by 17 00:01:49,610 --> 00:01:58,729 typing number equals, and double quotes 9 comma 2 2 3 comma 3 7 2 comma 0 3 6 18 00:01:58,729 --> 00:02:05,920 comma 8 5 4 comma 7 7 5 comma and 8 0 7, and we've got a closing double quote there. 19 00:02:05,920 --> 00:02:12,829 Now on line 9 if I type print parentheses number then square 20 00:02:12,829 --> 00:02:17,599 brackets again 1 colon colon 4, and closing off the 21 00:02:17,599 --> 00:02:24,799 right bracket and right parenthesis. Now if we run that, it doesn't appear to be very 22 00:02:24,799 --> 00:02:29,450 useful but it does illustrate using a step in slices. So it starts at position 1, 23 00:02:29,450 --> 00:02:34,640 which is the first comma, and it's slicing every fourth character. The list 24 00:02:34,640 --> 00:02:38,180 extends all the way to the end of the string and that's because we've omitted 25 00:02:38,180 --> 00:02:42,859 the stop value, and that gives us all the commas. So I said it didn't appear to be 26 00:02:42,859 --> 00:02:47,180 useful, however, it can be. In order to show you how it's useful, we're gonna have 27 00:02:47,180 --> 00:02:50,780 to use some things that we'll be looking at later. I don't like doing this 28 00:02:50,780 --> 00:02:54,680 generally, and I won't be doing it often, but I think something like that slice 29 00:02:54,680 --> 00:02:58,340 will make more sense if you can see a practical application of it. So what I'm 30 00:02:58,340 --> 00:03:02,480 going to do is start by changing some of the separators. At the moment they're all 31 00:03:02,480 --> 00:03:06,889 commas, but it's possible we may have to process a stream that contains a mix of 32 00:03:06,889 --> 00:03:11,540 separators. So what I'm going to do is use a mix of commas, semicolons, colons 33 00:03:11,540 --> 00:03:15,379 and spaces. These are all the things you might find used as separators when 34 00:03:15,379 --> 00:03:20,810 processing data. So we've got 9 comma 2 2 3. Let's change the comma 35 00:03:20,810 --> 00:03:25,579 after the 2 2 3 to a semicolon, and then moving on we've got, after 36 00:03:25,579 --> 00:03:30,829 3 7 2, we'll replace that comma with a colon. The next one after the O 3 6, 37 00:03:30,829 --> 00:03:34,970 we'll put a space there instead, and we'll leave the next one, 38 00:03:34,970 --> 00:03:37,970 8 5 4, leave that as a comma, and the one down the end here 39 00:03:37,970 --> 00:03:43,220 before the 8 0 7, we'll add a semicolon there as well. So if we run this program 40 00:03:43,220 --> 00:03:48,049 again now, we've changed those separators. You can see with the output there, we've 41 00:03:48,049 --> 00:03:53,690 actually got comma, semi colon, colon space, comma, semicolon. So why is that 42 00:03:53,690 --> 00:03:58,190 useful? Well if that number string represents seven values that appear in a 43 00:03:58,190 --> 00:04:03,949 data file, we can use the separator string to split out the seven values. Now 44 00:04:03,949 --> 00:04:06,799 this is the bit that I don't want you to worry about. Think of it as a 45 00:04:06,800 --> 00:04:11,320 demonstration. It's all stuff that you'll be learning about in later videos. 46 00:04:11,320 --> 00:04:15,199 So what I'm going to do is start by binding a variable to the slice instead of 47 00:04:15,199 --> 00:04:20,089 printing it out. So I'm going to change line 9 there. Instead of print, we're going 48 00:04:20,089 --> 00:04:26,389 to type separators is equal to, and I'll just remove the parenthesis on the end 49 00:04:26,389 --> 00:04:30,430 there, and then we're going to print separators. 50 00:04:30,430 --> 00:04:33,980 So we've now going a string containing all the separators that we used in 51 00:04:33,980 --> 00:04:38,090 numbers. Now it's not necessary to print it, but on line 10 I'm doing that anyway, 52 00:04:38,090 --> 00:04:41,660 just to confirm that we've got the separators, and obviously that should 53 00:04:41,660 --> 00:04:46,190 work because we've just only made a small change there, by binding it to the 54 00:04:46,190 --> 00:04:51,680 separators variable. Now we can use the separators to split out the individual 55 00:04:51,680 --> 00:04:55,640 values. This is the interesting part. So what I'm going to do is add that. I'm 56 00:04:55,640 --> 00:05:01,340 going to close down the run window, and on line 12 I'm going to type values is 57 00:05:00,840 --> 00:05:30,360 values = "".join(char if char not in separators else " " for char in number).split() 58 00:05:30,360 --> 00:05:33,780 Then on the next line 59 00:05:33,850 --> 00:05:49,420 print([int(val) for val in values]) 60 00:05:49,420 --> 00:05:54,140 Now I don't expect that code on lines 12 and 13 to make sense. Again, I'm using it to 61 00:05:54,140 --> 00:05:58,820 demonstrate why extracting every third character from a string might be useful. 62 00:05:58,820 --> 00:06:02,150 As you work through the course, you'll learn what this code's doing and you'll 63 00:06:02,150 --> 00:06:05,960 be able to write code like that for yourself. Now if you're typing the code in 64 00:06:05,960 --> 00:06:09,290 as you watch, you may want to copy and paste those two lines from the 65 00:06:09,290 --> 00:06:13,700 transcript for this video. The source code is also available in the resources 66 00:06:13,700 --> 00:06:16,940 for this video if you want to do that. It's very important that you use the 67 00:06:16,940 --> 00:06:21,560 correct type of brackets. The second one you see me use was a square bracket, and 68 00:06:21,560 --> 00:06:25,280 obviously, I'm using parentheses there, which some people also call brackets, 69 00:06:25,280 --> 00:06:29,870 as well. So basically, make sure you've typed it in exactly as you can see it 70 00:06:29,870 --> 00:06:36,110 here in order for it to work. Now if we run this program, and you can see the output 71 00:06:36,110 --> 00:06:41,930 is now showing us the seven values that we've extracted from the string, that 72 00:06:41,930 --> 00:06:46,489 we bound to the number variable on line 8. I think that's pretty impressive when 73 00:06:46,489 --> 00:06:49,309 you consider it's only a few lines of code there, and I'll just bring that back on 74 00:06:49,309 --> 00:06:53,839 the screen so you can see it. It's very hard to come up with real-world examples, 75 00:06:53,839 --> 00:06:58,369 when all we've covered so far in the course are variables, ints and strings, but 76 00:06:58,369 --> 00:07:02,899 hopefully, that demonstration has put the slice into a useful context. So make sure 77 00:07:02,899 --> 00:07:08,269 though, you understand how that slice on line 9 is working, and then I'll see 78 00:07:08,269 --> 00:07:11,599 you in the next video. And in that video we're going to look at slicing backwards. 79 00:07:11,599 --> 00:07:15,129 See you in the next video.