WEBVTT 0 00:00.950 --> 00:07.190 Now the next step and the next tip is pretty obvious when the editor is giving you an error, or when 1 00:07.190 --> 00:09.110 the console is giving you an error, 2 00:09.140 --> 00:11.840 fix the errors before you continue. 3 00:11.870 --> 00:17.450 Now, this is a little bit easier when you're dealing with errors in the editor, because you'll actually 4 00:17.450 --> 00:19.760 highlight you the line that's broken. 5 00:19.760 --> 00:21.920 So here we've got a print statement, 6 00:21.920 --> 00:27.650 and when we hover over it, it tells us that it expected an indented block. 7 00:27.650 --> 00:32.310 So that should be a good enough clue to tell us what's actually wrong. 8 00:32.340 --> 00:36.870 So if we go ahead and indent this block, then that error goes away. 9 00:36.870 --> 00:38.850 But that's not the only error, 10 00:38.880 --> 00:42.840 no, when you run this code, you still get another error. 11 00:42.840 --> 00:45.840 So let's say that I am a 12 year old girl, 12 00:46.650 --> 00:48.240 we get another error. 13 00:48.240 --> 00:56.280 And this error does not show up when we write the code, but it only shows up depending on what input 14 00:56.280 --> 00:58.770 we gave to this age variable. 15 00:58.770 --> 01:01.380 So now we have a different type of error. 16 01:01.380 --> 01:04.110 We have an error that's in the console. 17 01:04.440 --> 01:05.880 How do we solve this error. 18 01:05.880 --> 01:13.200 Well the easiest way is just to select the parts of the error that's not specific to your code, such 19 01:13.200 --> 01:17.700 as this part where it says 12 or our actual line of code. 20 01:17.700 --> 01:27.280 So if we go ahead and copy this part of our error and go into Google and paste it into the search 21 01:27.280 --> 01:33.640 box, and then we add our Python programming language, we should be able to figure out what is going 22 01:33.640 --> 01:34.240 on. 23 01:34.420 --> 01:38.110 So here is the exact same error that we have, 24 01:38.110 --> 01:42.610 and we have 17 answers explaining to us what could go wrong. 25 01:42.610 --> 01:50.680 And in this case it says the error message means that the string provided to this int conversion could 26 01:50.680 --> 01:55.180 not be parsed into an integer, so it couldn't be turned into an integer. 27 01:55.180 --> 02:01.120 And of course, the computer doesn't know how to turn 12 into the actual number 12, because you might 28 02:01.120 --> 02:05.890 have used even a different language, you might have used French, or you might have used German, right? 29 02:05.890 --> 02:07.780 So this doesn't actually work. 30 02:07.780 --> 02:12.560 And that should give us enough of a hint to know exactly what is going on. 31 02:12.560 --> 02:18.680 Now, of course, the easiest way is we could just tell the user to not do that, tell them to actually 32 02:18.680 --> 02:22.340 type numbers, and then we don't end up with that problem. 33 02:22.340 --> 02:26.030 But inevitably things might happen down the line, 34 02:26.030 --> 02:29.390 people might do something that is unexpected, 35 02:29.390 --> 02:36.860 so given that we have this weakness in our code, how can we actually fix our code to make it more durable? 36 02:37.550 --> 02:43.940 Well, one thing that I want to introduce you to for the first time here is the try-except block. 37 02:43.940 --> 02:48.200 So we can catch an exception using Python code. 38 02:48.200 --> 02:55.790 So the way that it works is we know that the potential error is something called a ValueError. 39 02:55.790 --> 03:03.540 So we can catch that error so that it doesn't crash our code and provide an alternative pathway for 40 03:03.540 --> 03:04.710 our code to go down. 41 03:04.830 --> 03:11.640 So the way that it works is we take the line of potentially dangerous code, which is this line where 42 03:11.640 --> 03:17.370 we convert a string that the user types in into an integer. 43 03:17.370 --> 03:20.970 And we've seen that that is what's causing this error here. 44 03:21.030 --> 03:25.800 So we take this line of code and we trap it inside a try block. 45 03:25.800 --> 03:28.200 So just the keyword try plus a colon, 46 03:28.200 --> 03:32.400 and then we indent this block of code to put it inside. 47 03:33.090 --> 03:35.100 So now we've got a try block. 48 03:35.100 --> 03:42.330 The next part is we need to add the 'except' keyword and then add in the exception that we want to catch. 49 03:42.330 --> 03:45.570 So in this case it's a ValueError that we're getting, 50 03:45.570 --> 03:47.820 and so that is what we're going to be catching. 51 03:47.820 --> 03:54.730 So now inside this except block, what we can do is we can say, well, what should happen if we end 52 03:54.730 --> 03:56.050 up with this error? 53 03:56.050 --> 04:01.660 So where the user types in something that we actually can't convert into an integer. 54 04:01.660 --> 04:06.130 Well let's first print something to tell them this is what's going on. 55 04:06.130 --> 04:11.560 For example, "You have typed in an invalid number. 56 04:11.680 --> 04:20.050 Please try again with a numerical response such as 15." 57 04:20.590 --> 04:24.910 So now we're giving them a little bit of feedback telling the user what's going on, 58 04:24.910 --> 04:30.010 and then we can just simply copy and paste this code here so that it runs again, 59 04:30.010 --> 04:32.260 and we give them another chance. 60 04:32.260 --> 04:37.990 So now let's run this code again and try with our previous offending code. 61 04:37.990 --> 04:43.190 And now you can see that we get our print statement giving us clear feedback 62 04:43.190 --> 04:44.150 what's wrong. 63 04:44.150 --> 04:47.600 And then it asks us how old are you? 64 04:47.600 --> 04:55.100 And now we can type in a number and continue our program as normal so it continues running instead of 65 04:55.100 --> 04:57.470 stopping our program and crashing it. 66 04:58.010 --> 05:06.710 But remember that solving the errors don't always solve all of your bugs like this. 67 05:06.740 --> 05:10.610 In this case, there are no errors with my code whatsoever, 68 05:10.610 --> 05:13.880 it's just not doing what I want it to do. 69 05:13.970 --> 05:19.160 And these are the most frustrating bugs to debug because nobody is helping you here. 70 05:19.160 --> 05:21.350 There's no errors that you can Google, 71 05:21.350 --> 05:23.810 there's no underlines that you can check, 72 05:23.810 --> 05:28.550 you actually have to rely on your skills as a programmer to fix this. 73 05:28.550 --> 05:35.370 So pause the video and see if you can fix the code so that instead of displaying the name of the variable, 74 05:35.370 --> 05:38.460 we actually get the value of the variable. 75 05:38.760 --> 05:39.900 Pause the video now. 76 05:43.650 --> 05:52.680 Now we of course know that this needs to be an f-string in order to insert that variable into this position 77 05:52.680 --> 05:54.300 in the curly braces, 78 05:54.450 --> 05:58.950 but if you didn't, then this would be a lot harder to debug. 79 05:59.520 --> 06:05.670 So experience comes in really handy with debugging, and the more bugs that you solve, the better you 80 06:05.670 --> 06:06.300 get at it. 81 06:07.080 --> 06:08.730 So go on to the internet. 82 06:08.730 --> 06:10.860 Try to help people on Stack Overflow. 83 06:10.860 --> 06:16.770 Go on to the discord channel for the course, try to solve other people's bugs and you will find yourself 84 06:16.770 --> 06:19.830 getting stronger and better day by day.