1 00:00:04,290 --> 00:00:08,138 Alright so in this video, we're going to make a small change to our code and see 2 00:00:08,138 --> 00:00:12,640 how it handles numbers that a user enters at the keyboard. I'm also going to 3 00:00:12,640 --> 00:00:16,570 take the opportunity to explain why we have to initialize separators on line 4 00:00:16,570 --> 00:00:21,520 2. I'm going to start with that in fact. Let's just remind ourselves what this 5 00:00:21,520 --> 00:00:26,289 program is doing by running it. I'm not debugging it this time. We've got the output at 6 00:00:26,289 --> 00:00:29,230 the bottom of the screen there, and basically the separators are printed 7 00:00:29,230 --> 00:00:33,160 out and the code produces a list of the seven numeric values contained in the 8 00:00:33,160 --> 00:00:38,110 number variable. So that works fine. The question we're looking at is, why have we 9 00:00:38,110 --> 00:00:43,120 bound separators to an empty string on line 2? Well let's comment that line 10 00:00:43,120 --> 00:00:47,800 out and see what happens when we run it. The first thing you'll notice is that 11 00:00:47,800 --> 00:00:51,940 we've got warnings wherever the value of separators is used in the code. So line 12 00:00:51,940 --> 00:00:55,690 6 over here, is trying to take the current value of separators and 13 00:00:55,690 --> 00:01:00,700 appending the char to it. The problem is that Python has no idea what the current 14 00:01:00,700 --> 00:01:04,720 value of separators is, and that's because we haven't bound separators to any value - 15 00:01:04,720 --> 00:01:09,880 it doesn't exist. If we hover over that, we can see name separators can be not 16 00:01:09,880 --> 00:01:14,840 defined. We need to create the separators variable by attaching it to a value, 17 00:01:14,840 --> 00:01:18,960 and that's what we're doing, effectively, on line 2. So if I run the program now 18 00:01:18,970 --> 00:01:24,789 with that line still commented out, you can see we actually get a crash there, 19 00:01:24,789 --> 00:01:29,470 name separators is not defined. So basically, we need to define our 20 00:01:29,470 --> 00:01:34,120 separators variable, by binding it to a value before we try to use its value. 21 00:01:34,120 --> 00:01:38,080 So that's really why line 2 is necessary. So I'd better uncomment that, I'll just 22 00:01:38,080 --> 00:01:42,640 undo that change to fix that, so that our program doesn't crash anymore. 23 00:01:42,640 --> 00:01:47,560 Alright so let's see how we can handle this code to get several values from the user. 24 00:01:47,560 --> 00:01:51,729 On line 1, what I'm going to do is change this to get input from the user, instead 25 00:01:51,729 --> 00:01:54,280 of actually using a string literal that we're currently doing. So I'm going to 26 00:01:54,280 --> 00:01:58,750 change it to be number equals input parenthesis double quotes 27 00:01:58,750 --> 00:02:10,360 Please enter a series of numbers using any separators you like colon and I better 28 00:02:10,360 --> 00:02:17,700 put my spelling head on, separators. Okay, so if we run the program now, 29 00:02:18,060 --> 00:02:29,600 and for the first example let's go with 1 comma 2 3 semicolon 4 5 6 : 7 8 9 0 1 2 30 00:02:29,600 --> 00:02:32,400 and what I'll also do is take the opportunity, I'll just go back and 31 00:02:32,410 --> 00:02:39,250 put a space after the first comma as well. 1 comma space 2 3 semicolon 4 5 6 32 00:02:39,250 --> 00:02:44,350 : 7 8 9 0 1 2, also noting here that all the values I've entered have a 33 00:02:44,350 --> 00:02:46,959 different number of digits. That's something that our slice 34 00:02:46,959 --> 00:02:51,580 wouldn't have been able to handle. So when I press ENTER here, we get a list 35 00:02:51,580 --> 00:02:57,250 containing the 4 values 1, 23, 456, 789012 36 00:02:57,250 --> 00:03:00,610 Remember that we're only interested in the for loop at the moment. Again, don't 37 00:03:00,610 --> 00:03:04,120 worry about understanding lines 10 and 11 at this time. I'm going to finish this 38 00:03:04,120 --> 00:03:07,660 video by making our program a bit more useful. Instead of just printing the 39 00:03:07,660 --> 00:03:11,260 values, I'll get the program to add them up and print out the total. Python's 40 00:03:11,260 --> 00:03:14,560 actually got a sum function built-in and you can find a list of the built-in 41 00:03:14,560 --> 00:03:22,000 functions, the link I'm going to put into a browser now. The link is also in 42 00:03:22,000 --> 00:03:26,830 the resources section. You can see sum, which is the one we're going to use, but 43 00:03:26,830 --> 00:03:30,610 again, you can check that at your leisure. Going back to the code, let's make a few 44 00:03:30,610 --> 00:03:35,230 changes. Firstly, I'm going to comment out line 8, then I'm gonna come down to line 45 00:03:35,230 --> 00:03:39,640 11. We're going to change this to calculate the sum. So to do that I'm 46 00:03:39,640 --> 00:03:44,560 going to add sum after the left parenthesis, with a left parenthesis, 47 00:03:44,560 --> 00:03:48,549 and right at the end I'm going to add another right parenthesis to make the 48 00:03:48,549 --> 00:03:54,190 line valid. If we run the code now, we've got a useful calculator for adding up a 49 00:03:54,190 --> 00:03:59,170 series of numbers. So we could do exactly the same as we did previously; 1 comma 50 00:03:59,170 --> 00:04:08,680 space 2 3 semicolon 4 5 6 colon 7 8 9 0 1 2. We've got a value there 789492, 51 00:04:08,680 --> 00:04:14,079 and run it again. You can use any separator you want with the numbers, 52 00:04:14,079 --> 00:04:19,329 so let's try another one; 1 comma 2 space 3 semicolon 4 colon 53 00:04:19,329 --> 00:04:28,880 space five space 6 space 7 comma 8 : 9 space 10. Press enter, 54 00:04:28,880 --> 00:04:33,140 and you can see, we get the value now of 55. the important bit about this code is the 55 00:04:33,150 --> 00:04:38,370 for loop on lines 4 through 6. That iterates over the input and builds up a 56 00:04:38,370 --> 00:04:42,450 string containing anything that isn't a numeric character. Because we're 57 00:04:42,450 --> 00:04:46,230 extracting the separators from the user's input, we don't then have to care 58 00:04:46,230 --> 00:04:51,260 about what separator characters they're using. This code is already quite robust. 59 00:04:51,260 --> 00:04:54,060 Have a go at entering all sorts of input and you'll find it's very 60 00:04:54,060 --> 00:04:57,990 difficult to crash the program. It is possible to crash it by holding down the 61 00:04:57,990 --> 00:05:01,650 control key, for example, but for normal input, it should cope with anything 62 00:05:01,650 --> 00:05:05,100 you can type. Moving forward in the next video, we'll look at iterating over 63 00:05:05,100 --> 00:05:10,400 another iterable type - the range. See you in the next video.