1 00:00:01,129 --> 00:00:06,899 Hi again! Let's have one more lecture about errors in Python and this 2 00:00:06,899 --> 00:00:11,429 particular lecture will be about handling errors. Handling errors can be 3 00:00:11,429 --> 00:00:16,590 an advanced concept to digest for now because you're still going through the 4 00:00:16,590 --> 00:00:22,199 basics of Python and you haven't seen any real application yet, but later 5 00:00:22,199 --> 00:00:27,990 will use error handling while we are building real-world applications so 6 00:00:27,990 --> 00:00:32,399 you're going to understand error handling better later on. For now let's 7 00:00:32,399 --> 00:00:35,670 just focus on the syntax and try to understand as much as you can 8 00:00:35,670 --> 00:00:42,899 I'll go and do an example here which I mentioned earlier. Let's say we have a 9 00:00:42,899 --> 00:00:54,090 function that does division between two given numbers like that. Return a divided 10 00:00:54,090 --> 00:00:59,719 by b and then you call the function here. Divide 1, 2. In this case the 11 00:01:05,640 --> 00:01:10,619 function will try to divide 1 by 2. And let me print out the output so that 12 00:01:10,619 --> 00:01:20,159 we can see it on the terminal. Go to the terminal and execute the script. So you 13 00:01:20,159 --> 00:01:28,460 get you get 0.5. Now that's good. However if the user enters let's say 14 00:01:28,460 --> 00:01:35,790 zero there like that, execute and your program will crash so it will show an 15 00:01:35,790 --> 00:01:41,939 error. Now this one here is an example of a longer error message that I mentioned 16 00:01:41,939 --> 00:01:45,750 previously in the previous videos that you might have more than one, more 17 00:01:45,750 --> 00:01:54,869 than one error in your traceback, so for instance this says line 4 at this line 18 00:01:54,869 --> 00:02:01,259 here. So that line is where Python captured the error at first 19 00:02:01,259 --> 00:02:06,360 so basically Python was trying to execute this line but it couldn't do it, 20 00:02:06,360 --> 00:02:10,709 it didn't manage to do it because this line was trying to get the information 21 00:02:10,709 --> 00:02:15,460 from this function and this function was trying to do this 22 00:02:15,460 --> 00:02:22,280 mathematical operation using zero after the division so that is not possible and 23 00:02:22,280 --> 00:02:27,950 Python is pointing that out here. So that's the main error in line two 24 00:02:27,950 --> 00:02:32,510 in this expression so that's where you should focus, however when you ask 25 00:02:32,510 --> 00:02:36,590 questions you should include the entire error message in your question 26 00:02:36,590 --> 00:02:43,550 as I mentioned previously. So back to handling errors now. What I'm 27 00:02:43,550 --> 00:02:49,850 trying to say here is that you know you have other functions here and other 28 00:02:49,850 --> 00:02:57,320 lines of code that you want to execute, that you want Python to execute, but if 29 00:02:57,320 --> 00:03:04,720 the user passed this zero number here the other lines would not be executed 30 00:03:04,720 --> 00:03:09,680 so your program would crash and you don't want that and the way to avoid 31 00:03:09,680 --> 00:03:17,720 that is by using try and accept so basically you try to capture the 32 00:03:17,720 --> 00:03:24,170 exception, to handle the exception. The way to do that is quite easy. 33 00:03:24,170 --> 00:03:33,860 You say try and return a/b, so this has to be indented like that so try is indented 34 00:03:33,860 --> 00:03:40,160 because it's under the function definition. And then return is indented 35 00:03:40,160 --> 00:03:49,190 because it's under the try expression. Then you have except, execute so this 36 00:03:49,190 --> 00:03:54,470 has to be on the same indentation level with try, they are the same block, so 37 00:03:54,470 --> 00:04:02,090 except if there is an exception. What you want to do is print out: "You are 38 00:04:02,090 --> 00:04:07,540 dividing by zero", or "�is this meaningless". So let me try 39 00:04:16,299 --> 00:04:26,380 this now and you get: "Zero division is meaningless" and none, oh sorry I meant 40 00:04:26,380 --> 00:04:34,420 to do here return, not print. I explained you why you get none there so you 41 00:04:34,420 --> 00:04:42,940 got none as an output because what the function did was its tried to do 42 00:04:42,940 --> 00:04:48,160 this expression but it got an error so it ignores this line, it doesn't 43 00:04:48,160 --> 00:04:54,880 execute it and then it goes to the next line. So this line is executed when 44 00:04:54,880 --> 00:05:01,540 this is not executed and so it printed out: "Zero division is meaningless", but it 45 00:05:01,540 --> 00:05:06,010 also printed out none because when you execute a function that doesn't have a 46 00:05:06,010 --> 00:05:10,450 return statement such as in this case we had the print statement here, the print 47 00:05:10,450 --> 00:05:15,820 function not the return statement, in that case if the function is not returning 48 00:05:15,820 --> 00:05:23,440 anything it can have a print function or other function as well, but if it 49 00:05:23,440 --> 00:05:29,229 doesn't have a return statement then it will print out none, so basically 50 00:05:29,229 --> 00:05:33,520 it executes the other procedures such as the print statement, it prints out the 51 00:05:33,520 --> 00:05:37,690 statement but if it doesn't have a return statement it doesn't, it prints 52 00:05:37,690 --> 00:05:43,030 out none. Anyway save this now, execute again and in this case you get only this 53 00:05:43,030 --> 00:05:48,729 zero division is meaningless printed out there. So basically if you had other 54 00:05:48,729 --> 00:05:57,280 lines of code here like that, those would be executed as well and that happens by 55 00:05:57,280 --> 00:06:03,160 using the try and except block who which make sure that the code flow continues. 56 00:06:03,160 --> 00:06:11,050 So while the important thing to note is that it is advisable to actually here use 57 00:06:11,050 --> 00:06:18,120 the exact name of the error that you want to accept, so 58 00:06:19,350 --> 00:06:27,340 Zero Division Error and as you see these got turned into blue which means that 59 00:06:27,340 --> 00:06:33,370 this is actually a Python keyword, is recognized by Python and in that case if 60 00:06:33,370 --> 00:06:41,560 you exact you this you get the same output actually like that or if you pass 61 00:06:41,560 --> 00:06:46,650 a number there that it is possible to get a division from, you'll get that. 62 00:06:46,650 --> 00:06:53,020 Sorry about the backslash. I typed that by mistake on my terminal. Execute 63 00:06:53,020 --> 00:06:56,650 again so you get this. And so what I'm trying to say about the zero division 64 00:06:56,650 --> 00:07:01,090 error is that you know sometimes you might get other types of errors in your 65 00:07:01,090 --> 00:07:07,930 code, other types of exceptions. Let's say you have a name error there 66 00:07:07,930 --> 00:07:12,370 and you are saying that except all errors when you don't pass this you 67 00:07:12,370 --> 00:07:17,919 you're basically including all types of errors there and that is a bit dangerous for your 68 00:07:17,919 --> 00:07:22,960 code because you know you might have problems that you don't notice and 69 00:07:22,960 --> 00:07:27,789 basically you are ignoring that, but you shouldn't. So you should be specific 70 00:07:27,789 --> 00:07:32,830 there, explicit like that. If there are other types of errors such as a name error, 71 00:07:32,830 --> 00:07:38,349 that name error will crash your program, so you know what's going on. 72 00:07:38,349 --> 00:07:42,760 You need to be specific. If you want to handle that error too, then 73 00:07:42,760 --> 00:07:47,380 you can add another exception here. Except name error for instance. Yeah, 74 00:07:47,380 --> 00:07:52,389 that's about handling errors in Python. I hope this makes sense! I hope I explained 75 00:07:52,389 --> 00:07:58,330 this well! And yeah, this is about errors. I'll talk to you in the next lectures. 76 00:07:58,330 --> 00:08:00,000 See you!