1 00:00:04,680 --> 00:00:09,330 So running our high-low game in the debugger can be a bit slow. The loop is 2 00:00:09,330 --> 00:00:12,959 only going around 10 times, but if we had a much larger range of numbers, you'd 3 00:00:12,959 --> 00:00:16,379 soon get pretty bored clicking the Step Over button. When I ran the program 4 00:00:16,379 --> 00:00:21,860 in the last video, things really only got interesting when the computer guessed 99. 5 00:00:21,860 --> 00:00:25,349 What would be really good would be if we could get the debugger to stop at that 6 00:00:25,349 --> 00:00:32,159 point, when guess is 99. Luckily, we can do just that. I'll show you, now, how to do 7 00:00:32,159 --> 00:00:36,329 that with both IntelliJ and PyCharms debuggers. But if you're using a 8 00:00:36,329 --> 00:00:39,710 different IDE, your debugger may well have a similar feature. 9 00:00:39,710 --> 00:00:44,070 Unfortunately, the idle debugger doesn't have conditional breakpoints, which is 10 00:00:44,070 --> 00:00:47,520 what we need here. So if you're using IDLE, you'll have to step over your code in 11 00:00:47,520 --> 00:00:51,879 the usual way. So to achieve this, firstly, set a 12 00:00:51,879 --> 00:00:56,469 breakpoint on line eight, which is our while loop, and we're not interested in 13 00:00:56,469 --> 00:01:00,100 seeing the first few lines being executed. The debugger's going to stop each 14 00:01:00,100 --> 00:01:04,720 time the loop goes around, which isn't really what we want. We're really only 15 00:01:04,720 --> 00:01:09,280 interested in what happens once low and high are equal. So to set a condition on 16 00:01:09,280 --> 00:01:14,740 a breakpoint, right-click the breakpoint dot in the margin. Now the condition that 17 00:01:14,740 --> 00:01:19,840 we want here, typing into this field, is low is equal to high. So I'm going to 18 00:01:19,840 --> 00:01:24,850 type low equal high - remember to use two equal signs, and I'm gonna click Done 19 00:01:24,850 --> 00:01:28,720 once I've done that. So notice that there's now a little question mark next 20 00:01:28,720 --> 00:01:33,610 to the red dot, as well, to indicate that it's a conditional breakpoint. So I'm gonna start 21 00:01:33,610 --> 00:01:36,840 the debugger, as we would normally do, 22 00:01:37,820 --> 00:01:42,320 and you saw me right click in the editor pane and choose debug. I like to do that, 23 00:01:42,320 --> 00:01:45,280 as per normal, because that makes sure that I'm debugging the correct file, 24 00:01:45,280 --> 00:01:48,360 because you might have a different file selected up here. In which case, it would 25 00:01:48,360 --> 00:01:53,880 be invoking that file and not this one. In any event, debugger test per normal, 26 00:01:53,880 --> 00:01:57,819 press ENTER to start. Alright so I'm going to use the same number as we did 27 00:01:57,819 --> 00:02:02,440 in the last video - 100. So I need to go through and let the computer pick, 28 00:02:02,440 --> 00:02:14,600 so it's gonna be lower - I'll just go through and do this. So far, the 29 00:02:14,600 --> 00:02:20,260 breakpoint hasn't been hit yet, but it'll do that as soon as I enter h now, to go 30 00:02:20,260 --> 00:02:27,370 higher. I do that, you can see what's happened there. We stopped on line eight 31 00:02:27,370 --> 00:02:31,930 and low does equal high. We can see both values there, in the variables pane at 32 00:02:31,930 --> 00:02:35,379 the bottom of the screen, for low and for high. So that means the condition will 33 00:02:35,379 --> 00:02:39,129 now evaluate to false, and the while loop will terminate. If we click Step 34 00:02:39,129 --> 00:02:44,560 Over, let's just check that that does happen. You can see that did happen. Basically, 35 00:02:44,560 --> 00:02:48,519 because the while loop terminated normally, we didn't break out of it. Execution is 36 00:02:48,519 --> 00:02:52,660 continuing in the else block. As you can see, sitting on line 30. We switch to the 37 00:02:52,660 --> 00:02:58,500 console tab. If I click on resume program now, 38 00:02:58,560 --> 00:03:01,980 you see we've got the last two lines of output there. So we should do that again, this 39 00:03:01,980 --> 00:03:05,850 time with a number that doesn't cause low and high to become equal. So I'm 40 00:03:05,850 --> 00:03:11,580 going to set a breakpoint on the break statement on line 23. Okay, I'm gonna start the 41 00:03:11,580 --> 00:03:21,270 debugger again, enter to start. This time my number's going to be 250, so I'm gonna 42 00:03:21,270 --> 00:03:26,280 press Enter, which I've done, and I'm going to lower. This time that answer is correct 43 00:03:26,280 --> 00:03:31,590 so I'm going to press c for correct, and we've now hit the breakpoint, as you can 44 00:03:31,590 --> 00:03:35,250 see, so the debugger stops on our breakpoint now, on line 23. We're about to 45 00:03:35,250 --> 00:03:40,650 break out of the loop. So that means that the else block won't be executed. Go back 46 00:03:40,650 --> 00:03:48,380 to the console tab - we can see that the computer got it in two guesses. So we use Step Over - 47 00:03:48,380 --> 00:03:51,780 that confirms that the else block isn't executed. There's no more code and 48 00:03:51,780 --> 00:03:57,000 the program's terminated, as you can see. Alright, so that's what else does when 49 00:03:57,000 --> 00:04:01,560 used with a loop. Because python reuses the word else for this, it can be 50 00:04:01,560 --> 00:04:05,550 confusing. It would have been a lot clearer if Python used something that, 51 00:04:05,550 --> 00:04:08,430 perhaps, made a bit more sense - something like, instead of else, perhaps 52 00:04:08,430 --> 00:04:16,839 completed. That would probably have made a lot more sense, or perhaps, no break. 53 00:04:16,839 --> 00:04:20,120 But unfortunately, that's not the case. It doesn't use either of those - it uses else - 54 00:04:20,130 --> 00:04:24,030 so I'll just undo both of those and go back to what we had. But at this point, 55 00:04:24,030 --> 00:04:28,680 you do now know what else does when used in a for or a while loop. You don't have 56 00:04:28,680 --> 00:04:31,890 to use it in your own code, but you may come across it in code that you have to 57 00:04:31,890 --> 00:04:35,980 work with, and now hopefully, you've got a good understanding of what it does. 58 00:04:35,980 --> 00:04:39,000 Alright, so in the next video, we're going to see else used in an earlier example 59 00:04:39,000 --> 00:04:44,000 from this section. See you in the next video.