1 00:00:04,720 --> 00:00:09,070 Back in the previous section, we used a slice to extract all the delimiters 2 00:00:09,070 --> 00:00:12,880 from a list of numbers. I'm going to start by reviewing that code, and I've 3 00:00:12,880 --> 00:00:16,509 called this file strings2.py and I've grabbed that code from that previous 4 00:00:16,509 --> 00:00:19,810 section and you can see it on the screen there. What I have done, though, is deleted 5 00:00:19,810 --> 00:00:23,769 the first few lines of code from the file. We used a slice that started at 6 00:00:23,769 --> 00:00:28,929 position 1, which is the first comma, then extracted every fourth character until 7 00:00:28,929 --> 00:00:32,800 it reached the end of the string. That worked but it does rely on there being 8 00:00:32,800 --> 00:00:37,030 three digits in each of the numbers, after the first one. That's probably fine 9 00:00:37,030 --> 00:00:40,660 if the data came from another computer program, but it's not something we can 10 00:00:40,660 --> 00:00:46,329 rely on if the user's typing in those numbers. In that case, we should examine 11 00:00:46,329 --> 00:00:50,829 each character in the number string to check if it's a digit or not. As you saw 12 00:00:50,829 --> 00:00:54,910 in the previous video, a for loop can be used to do that. What we're going to do 13 00:00:54,910 --> 00:00:59,170 here is iterate over numbers and append anything that isn't a digit to the 14 00:00:59,170 --> 00:01:03,460 separators string. Once we've seen the code working, we'll step through it with 15 00:01:03,460 --> 00:01:07,869 a debugger so you can see what it's doing. The first step is to initialise 16 00:01:07,869 --> 00:01:12,580 our separators variable. That's something that causes a lot of confusion, and I'm going 17 00:01:12,580 --> 00:01:16,990 to spend a minute discussing it, once we've seen the code working. So I'm going 18 00:01:16,990 --> 00:01:23,170 to change this to become equal to an empty string, and I'm gonna come down here 19 00:01:23,170 --> 00:01:28,959 and add some code, specifically starting on line 4; for char in number 20 00:01:28,959 --> 00:01:37,119 colon if not char.isnumeric and the parentheses are added automatically, 21 00:01:37,119 --> 00:01:45,819 colon separators equals separators plus char. We're going to leave the code on line 22 00:01:45,819 --> 00:01:49,239 8 that prints the separators and the rest of the file is going to remain as 23 00:01:49,239 --> 00:01:54,099 it was. Alright so I've used another one of the string methods here on line 24 00:01:54,099 --> 00:01:57,910 5. I provided a link to the string methods earlier in this section and we'll 25 00:01:57,910 --> 00:02:02,640 be looking at a few of them in our examples. isnumeric will return True if 26 00:02:02,640 --> 00:02:06,459 the character is a number, and False otherwise. We want to add things that 27 00:02:06,460 --> 00:02:12,080 aren't a digit, which is why the condition becomes if not char.isnumeric 28 00:02:12,080 --> 00:02:16,020 Alright so I'm going to run the program to make sure that it works. 29 00:02:16,880 --> 00:02:21,060 So the first thing we get printed out is the string containing all the separators. 30 00:02:21,060 --> 00:02:24,120 Now that was printed by the code on line 8. I'm just going to move this down so we 31 00:02:24,120 --> 00:02:28,470 can see a bit more code. These strings created by our for loop on lines 4 32 00:02:28,470 --> 00:02:33,300 through 6. Now we use that string of separators on line 10 to get the 33 00:02:33,300 --> 00:02:37,140 individual numbers. Once again, don't worry about the lines 10 and 11 at the 34 00:02:37,140 --> 00:02:40,500 moment, you'll learn all about them later. At the moment, we're just using them to 35 00:02:40,500 --> 00:02:44,610 show why we want to extract all the separators from number. Alright so our 36 00:02:44,610 --> 00:02:48,959 program works, but how? What we'll do is we'll set a breakpoint on the for loop, 37 00:02:48,960 --> 00:02:57,820 line 4 over here, and let's run the program in the debugger. 38 00:02:57,820 --> 00:03:03,380 In the variables pane we can see the value of number. So it's a string containing 7 numbers, separated by 39 00:03:03,390 --> 00:03:08,489 various separated characters. Below that we can see that the variable separators 40 00:03:08,489 --> 00:03:12,600 is currently bound to an empty string. Two quotes with nothing between them is 41 00:03:12,600 --> 00:03:16,440 an empty string. As I said, I'll come back to that later. Now when I step over the 42 00:03:16,440 --> 00:03:20,880 code, which I'll do now, you can see that the variable char gets the first 43 00:03:20,880 --> 00:03:25,019 character from the string. That's the digit 9. We're about to test if it's a 44 00:03:25,019 --> 00:03:30,209 digit, so I'm going to step over line 5 to do that. The character 9 does 45 00:03:30,209 --> 00:03:34,860 represent a number so isnumeric returns True. We're checking for not isnumeric, 46 00:03:34,860 --> 00:03:39,930 which is False, so therefore the code on line 6 is skipped. Alright so we're 47 00:03:39,930 --> 00:03:44,850 back now on line 4. I'm gonna step over again. char now gets the next character from 48 00:03:44,850 --> 00:03:48,870 number which is a comma, as you can see. A comma obviously doesn't represent a 49 00:03:48,870 --> 00:03:53,820 number and each numeric should return False. Not False is True and we should 50 00:03:53,820 --> 00:03:59,190 get line 6 executed this time. Let's step over to check that, and that's good. Line 51 00:03:59,190 --> 00:04:02,670 6 is about to be executed. When you're using the debugger like this, always 52 00:04:02,670 --> 00:04:06,620 spend time working out what's going to happen before it does. 53 00:04:06,620 --> 00:04:11,040 That'll really help you to learn how to read code without ultimately having to run it in 54 00:04:11,040 --> 00:04:16,140 the debugger. Ok separators is currently an empty string. Line 6 will append the 55 00:04:16,140 --> 00:04:19,649 value of char to it, which should result in separators becoming a string 56 00:04:19,649 --> 00:04:25,860 containing a comma. Let's step over and see. In the variables pane, separators is 57 00:04:25,860 --> 00:04:30,390 a comma. So we've seen how char is getting each of the characters in turn 58 00:04:30,390 --> 00:04:34,530 and we really don't need to keep watching line 4. We've also said that line 6 59 00:04:34,530 --> 00:04:39,210 is only executed when we get a character that's not numeric. So it's line 6 that 60 00:04:39,210 --> 00:04:43,230 we're really interested in here. We can debug more efficiently by clearing the 61 00:04:43,230 --> 00:04:50,300 breakpoint on line 4 and setting one on line 6 instead, like so. 62 00:04:50,300 --> 00:04:54,380 When we've done that, we can use the button that looks like a typical video player icon, 63 00:04:54,390 --> 00:04:59,520 a vertical bar on a triangle. That's this button over here, resume program, and what 64 00:04:59,520 --> 00:05:02,940 that will do is run our code at full speed until it hits our breakpoint. 65 00:05:02,940 --> 00:05:07,920 So I'm going to click that button now and the debugger executes the code for the 2, 2 66 00:05:07,920 --> 00:05:13,410 and 3 in number, and char now contains a semicolon. That's obviously 67 00:05:13,410 --> 00:05:17,400 not numeric and that's why we've got our breakpoint hit on line 6. When I 68 00:05:17,400 --> 00:05:21,660 execute that line, which I'll come over here and step over, we can see that the 69 00:05:21,660 --> 00:05:25,980 semicolon is appended to separators. In the variables pane, separators now has 70 00:05:25,980 --> 00:05:30,720 two characters; a comma and a semicolon. Now it can be easier to see the values in 71 00:05:30,720 --> 00:05:34,800 the editor pane. This IDE shows them in grey, as you can see up there. At the end of 72 00:05:34,800 --> 00:05:37,920 line 2 we've got the comma and the semicolon. We've also got the current 73 00:05:37,920 --> 00:05:42,600 value of char at the end of line 4. Alright so I'm going to resume the program 74 00:05:42,600 --> 00:05:47,260 again by clicking on the icon, and that ran past the 3, 7 and 2. 75 00:05:47,260 --> 00:05:51,920 char, as you can see, is now a colon, and line 6 will cause that to be appended to our 76 00:05:51,930 --> 00:05:56,700 separator string when I step over, which I'll do now. You can see the colon has 77 00:05:56,700 --> 00:06:01,830 been added to separators now. Next we should get a comma, the one before 7 78 00:06:01,830 --> 00:06:07,140 7 5, so let's resume. It actually forgot about the space there, you can see 79 00:06:07,140 --> 00:06:10,830 that, obviously, we had a space in the string which is non numeric. So we've hit 80 00:06:10,830 --> 00:06:15,300 that, so therefore a space should be added to our string if I step over which 81 00:06:15,300 --> 00:06:19,830 I'll do now, and you can see the string, the space rather, has been added to our 82 00:06:19,830 --> 00:06:24,330 separators variable. If I come over now and click on resume, next we should get a 83 00:06:24,330 --> 00:06:30,270 comma and that's the one that's just before the 775. Resume program, we've got a comma 84 00:06:30,270 --> 00:06:34,980 in char now. If I step over you can see that's added to our separators variable, 85 00:06:34,980 --> 00:06:39,150 and resume one more time. This time, as the last one that we'll match, we 86 00:06:39,150 --> 00:06:42,840 should get the semicolon which is before the 807, and there's obviously no other 87 00:06:42,840 --> 00:06:47,130 characters. I'll click on resume. We've got the semicolon and step over 88 00:06:47,130 --> 00:06:53,040 once more and that's been added to our separators variable. The remaining three 89 00:06:53,040 --> 00:06:56,340 characters at this point are all numeric, and that means that we shouldn't get to 90 00:06:56,340 --> 00:06:59,880 line 6 again and resuming the program, which I'll do now, should cause it to run 91 00:06:59,880 --> 00:07:04,560 through to the end. And you can see that's been the case there. Now if you 92 00:07:04,560 --> 00:07:07,710 want to use step over until the program terminates instead of resume program, 93 00:07:07,710 --> 00:07:11,310 that I used there, to be sure about what's happening then go ahead. It's really 94 00:07:11,310 --> 00:07:14,640 helpful to see each line being executed when you're learning. As you can see there, 95 00:07:14,640 --> 00:07:18,740 I pressed resume program. The program ended. We click over to the console now, we can 96 00:07:18,750 --> 00:07:22,650 see the output on screen. We've got our separators printed out, followed by a 97 00:07:22,650 --> 00:07:26,220 list containing the seven values in number. So I'm going to stop the video 98 00:07:26,220 --> 00:07:29,820 here but you might want to step through the code a few more times, just to make 99 00:07:29,820 --> 00:07:33,420 sure you understand what it's doing. And as a reminder, don't worry about lines 10 100 00:07:33,420 --> 00:07:36,730 and 11. They're quite advanced and won't make much sense at this point in the course. 101 00:07:36,730 --> 00:07:41,190 In the next video, we'll see how a code can handle values that a user 102 00:07:41,190 --> 00:07:45,350 types in. See you in the next video.