1 00:00:00,840 --> 00:00:02,160 Instructor: In this exercise, 2 00:00:02,160 --> 00:00:04,920 we're going to bake some pies. 3 00:00:04,920 --> 00:00:07,770 If you take a look at the starting code, 4 00:00:07,770 --> 00:00:12,770 you'll see that we're taking the input as a list of fruits 5 00:00:13,140 --> 00:00:16,379 and we're putting it into our code, 6 00:00:16,379 --> 00:00:21,380 and on line 11, we call the function make pie 7 00:00:22,410 --> 00:00:27,410 and tell it which pie out of our list of fruits to make. 8 00:00:27,840 --> 00:00:32,790 So if make pie zero, then that would be to make apple pie, 9 00:00:32,790 --> 00:00:35,310 make pie one, that should be a pear pie, 10 00:00:35,310 --> 00:00:37,830 make pie two, that should be an orange pie. 11 00:00:37,830 --> 00:00:40,530 Now, unfortunately, we are providing a index 12 00:00:40,530 --> 00:00:44,820 that is way out of range of our list of fruits. 13 00:00:44,820 --> 00:00:46,230 It's like we're trying to make a pie 14 00:00:46,230 --> 00:00:49,200 with a fruit type that doesn't exist. 15 00:00:49,200 --> 00:00:51,052 This normally would crash our code, 16 00:00:51,052 --> 00:00:54,450 and indeed, if you just try running the code as it is 17 00:00:54,450 --> 00:00:55,770 with the starting code, 18 00:00:55,770 --> 00:01:00,000 you will see the errors in the output area. 19 00:01:00,000 --> 00:01:04,709 Your job is to update the make pie function 20 00:01:04,709 --> 00:01:06,810 so that in the case where the user 21 00:01:06,810 --> 00:01:09,390 does something silly like this on line 11 22 00:01:09,390 --> 00:01:12,600 where they try to pick a fruit that does not exist 23 00:01:12,600 --> 00:01:14,580 in our list of fruits, 24 00:01:14,580 --> 00:01:17,010 then instead of crashing the program, 25 00:01:17,010 --> 00:01:19,710 we're just going to print "fruit pie". 26 00:01:19,710 --> 00:01:21,690 So we don't know what fruit you want, 27 00:01:21,690 --> 00:01:24,210 we're just gonna tell you we just made some fruit pie 28 00:01:24,210 --> 00:01:26,490 and tell the user to go away. 29 00:01:26,490 --> 00:01:28,770 But this is a really important skill, 30 00:01:28,770 --> 00:01:31,050 the way that we can handle errors 31 00:01:31,050 --> 00:01:35,430 instead of allowing it to crash our application. 32 00:01:35,430 --> 00:01:37,380 Take a look in the description pane, 33 00:01:37,380 --> 00:01:39,300 look at the example input 34 00:01:39,300 --> 00:01:42,750 and what the example output is expected, 35 00:01:42,750 --> 00:01:47,223 and write some code to catch this exception. 36 00:01:48,060 --> 00:01:48,893 Have a go now. 37 00:01:56,340 --> 00:01:59,760 The first thing we do is using a try block, 38 00:01:59,760 --> 00:02:01,260 we catch the line of code 39 00:02:01,260 --> 00:02:05,880 that is potentially going to cause us an error, 40 00:02:05,880 --> 00:02:09,150 and in this case, it is the line on line seven 41 00:02:09,150 --> 00:02:12,150 where we try to access the list of fruits 42 00:02:12,150 --> 00:02:15,630 at an index that may or may not exist. 43 00:02:15,630 --> 00:02:18,930 When we call line 13, make pie four, 44 00:02:18,930 --> 00:02:21,810 we pass four into line seven 45 00:02:21,810 --> 00:02:26,070 and we try to access our list of fruits at index four. 46 00:02:26,070 --> 00:02:27,750 So that obviously doesn't exist. 47 00:02:27,750 --> 00:02:29,520 Index three doesn't even exist. 48 00:02:29,520 --> 00:02:32,340 There's only three items in our list. 49 00:02:32,340 --> 00:02:34,230 So this line, line seven, 50 00:02:34,230 --> 00:02:36,840 is the one that causes the index error, 51 00:02:36,840 --> 00:02:38,580 and that's the one that we are penning in 52 00:02:38,580 --> 00:02:41,463 in this safe environment under try. 53 00:02:43,050 --> 00:02:46,830 The next part is where we have our exception. 54 00:02:46,830 --> 00:02:48,750 We know from running the code, 55 00:02:48,750 --> 00:02:51,870 the type of exception we get is an index error, 56 00:02:51,870 --> 00:02:55,320 and this is the exception that we wanna handle in this case. 57 00:02:55,320 --> 00:02:57,780 Now, there can be many, many other types 58 00:02:57,780 --> 00:02:59,310 of errors and exceptions. 59 00:02:59,310 --> 00:03:02,040 We don't want to handle all of them in this way 60 00:03:02,040 --> 00:03:03,150 because there might be things 61 00:03:03,150 --> 00:03:05,580 that we haven't even predicted that's wrong. 62 00:03:05,580 --> 00:03:07,950 The only thing that we know that could go wrong 63 00:03:07,950 --> 00:03:10,260 that we wanna handle is the index error. 64 00:03:10,260 --> 00:03:12,870 So we have except index error, 65 00:03:12,870 --> 00:03:14,880 and when this error does happen, 66 00:03:14,880 --> 00:03:17,520 we're going to print fruit pie 67 00:03:17,520 --> 00:03:19,983 instead of crashing our application. 68 00:03:21,690 --> 00:03:23,580 Finally, we have an else block 69 00:03:23,580 --> 00:03:27,450 that catches the case where there are no exceptions, 70 00:03:27,450 --> 00:03:30,120 and in this case, we're just going to do our usual, 71 00:03:30,120 --> 00:03:33,810 which is to print the name of the fruit from the list 72 00:03:33,810 --> 00:03:36,153 that is picked plus the word pie. 73 00:03:37,050 --> 00:03:40,290 And this block of code now in make pie 74 00:03:40,290 --> 00:03:44,700 is now safe against the potential index error. 75 00:03:44,700 --> 00:03:46,854 If the user changes line 13 76 00:03:46,854 --> 00:03:49,860 to say make pie one, make pie two, 77 00:03:49,860 --> 00:03:52,410 it's going to function as expected, 78 00:03:52,410 --> 00:03:55,500 printing out the name of the fruit and the word pie, 79 00:03:55,500 --> 00:03:57,060 but if they make a mistake 80 00:03:57,060 --> 00:04:00,900 and happen to go out of the range, of the list, 81 00:04:00,900 --> 00:04:03,330 then we're just going to print fruit pie. 82 00:04:03,330 --> 00:04:06,270 There's no crashes, there's no alarm bells, 83 00:04:06,270 --> 00:04:09,900 everything is all safe and all handled, 84 00:04:09,900 --> 00:04:12,960 which is the point of our exception handling. 85 00:04:12,960 --> 00:04:14,700 And this is a really important skill, 86 00:04:14,700 --> 00:04:17,370 if not a little bit neglected by developers 87 00:04:17,370 --> 00:04:19,890 because it's not fun thinking about edge cases 88 00:04:19,890 --> 00:04:21,630 and handling them each time. 89 00:04:21,630 --> 00:04:23,970 But this is an important skill on your road 90 00:04:23,970 --> 00:04:26,073 to becoming a professional developer.