1 00:00:00,810 --> 00:00:02,160 So in the last lesson, 2 00:00:02,190 --> 00:00:07,190 we looked at how we can use this JSON format to save our data and to load 3 00:00:09,120 --> 00:00:11,070 our data into our program. 4 00:00:11,730 --> 00:00:16,730 But one of the problems that we have is if we run our program from scratch 5 00:00:17,280 --> 00:00:21,600 where we don't have that data.json file created, 6 00:00:21,930 --> 00:00:26,930 then the first thing that it's going to encounter once it lands inside here is 7 00:00:27,120 --> 00:00:30,570 it's going to try and open a file that doesn't exist. 8 00:00:31,110 --> 00:00:34,050 And what happens then? We get a file 9 00:00:34,050 --> 00:00:38,490 not found error because there is no such file data.json. 10 00:00:39,030 --> 00:00:41,400 So what can we do? Well, 11 00:00:41,640 --> 00:00:46,640 we already learned about dealing with exceptions and handling them so that we 12 00:00:47,160 --> 00:00:49,380 don't end up in these situations. 13 00:00:49,980 --> 00:00:54,980 So now it's time to put your knowledge into practice inside a real project. 14 00:00:55,650 --> 00:01:00,650 And I want you to think about how you can catch that particular exception, 15 00:01:01,380 --> 00:01:06,060 how you can get it to work so that if this fails, 16 00:01:06,330 --> 00:01:09,780 then we simply create a brand new data file. 17 00:01:10,200 --> 00:01:13,530 But if it does work, then we can simply load up the data, 18 00:01:13,860 --> 00:01:16,050 update the data and write the data. 19 00:01:16,680 --> 00:01:19,830 So the actual implementation I'll leave up to you. 20 00:01:20,220 --> 00:01:25,220 But what you want to be able to do is to not have a data.json file and run 21 00:01:26,190 --> 00:01:28,380 your code, and it would not crash 22 00:01:28,500 --> 00:01:33,500 and instead it would create a brand new data.json file with the new data. 23 00:01:35,640 --> 00:01:40,640 But if you had already got some old data, then it should simply just update and 24 00:01:40,770 --> 00:01:45,600 write it to file. Pause the video and see if you can complete this 25 00:01:45,720 --> 00:01:46,590 as a challenge. 26 00:01:50,970 --> 00:01:55,200 This always starts with analyzing which part of our code is the part that's 27 00:01:55,200 --> 00:01:59,400 going to fail or likely to fail at some point. And in our case, 28 00:01:59,460 --> 00:02:00,960 it's this line right here, 29 00:02:01,140 --> 00:02:06,140 opening this line in read mode is dangerous because if this doesn't exist, 30 00:02:07,260 --> 00:02:09,720 then we get that file not found error. 31 00:02:10,259 --> 00:02:15,090 So what we can do is we can put this inside a try statement. 32 00:02:15,660 --> 00:02:20,010 Try opening this file and try reading the data that's inside. 33 00:02:20,790 --> 00:02:24,630 Now, if this fails, however, then we can catch it 34 00:02:25,110 --> 00:02:28,230 and we're going to catch a very specific type of exception, 35 00:02:28,260 --> 00:02:32,250 which is the file not found error exception. Now, 36 00:02:32,250 --> 00:02:34,050 when this exception happens, 37 00:02:34,230 --> 00:02:38,490 what we want to do is we want to create a new file 38 00:02:38,820 --> 00:02:43,740 which is going to be our data.json. So at this point, 39 00:02:43,740 --> 00:02:48,090 remember it doesn't yet exist. And we're going to open it in write mode. 40 00:02:48,750 --> 00:02:53,490 And this data file is going to be used so that we can write to it 41 00:02:53,520 --> 00:02:57,810 and we can dump our newly created data up here. 42 00:02:58,350 --> 00:03:01,480 Remember, when the user hits the add button, 43 00:03:01,780 --> 00:03:06,190 then everything they've typed in these entries gets aggregated into this 44 00:03:06,190 --> 00:03:07,023 dictionary 45 00:03:07,210 --> 00:03:11,710 and that dictionary is what we want to dump into this new data file. 46 00:03:12,340 --> 00:03:16,900 So we'll get hold of that new data and we'll dump it into the data file. 47 00:03:17,830 --> 00:03:18,550 And again, 48 00:03:18,550 --> 00:03:23,550 we'll keep the indent to four spaces just so that we can read it more easily. 49 00:03:25,030 --> 00:03:28,750 Now this is what should happen if the file's not found. 50 00:03:29,380 --> 00:03:33,250 But if the file was found and it already exists, 51 00:03:33,340 --> 00:03:37,240 then we're going to tap into the else statement. And in the else statement 52 00:03:37,270 --> 00:03:42,070 what we're going to do is we're going to get hold of the data which we managed 53 00:03:42,070 --> 00:03:46,270 to get because this block of code succeeded, and in the else block 54 00:03:46,270 --> 00:03:50,950 what we're going to do is we're going to update the data with the new data. Now, 55 00:03:51,100 --> 00:03:53,500 this else block is only going to be triggered 56 00:03:53,530 --> 00:03:56,650 if everything inside the try block was successful. 57 00:03:57,070 --> 00:03:59,260 So that means by the end of this block, 58 00:03:59,290 --> 00:04:04,290 we have this data which holds onto all of the existing data from that data file 59 00:04:05,020 --> 00:04:09,670 and we update that data with the new data which is this dictionary here. 60 00:04:10,360 --> 00:04:13,210 Now, after we've updated that data, 61 00:04:13,270 --> 00:04:17,560 we want to be able to open up data.jason in the write mode 62 00:04:17,950 --> 00:04:22,950 and then dump this updated data from here into that data file. 63 00:04:25,480 --> 00:04:27,940 And then once all of this is done, 64 00:04:28,570 --> 00:04:32,980 no matter if there was an exception or if there was no issues, 65 00:04:33,280 --> 00:04:37,840 we're going to still need to delete everything that's inside the website and 66 00:04:37,840 --> 00:04:38,800 password entry. 67 00:04:39,220 --> 00:04:43,240 So we can even add a finally keyword right here. 68 00:04:44,560 --> 00:04:49,360 So this is the final code that deals with our exception. 69 00:04:49,690 --> 00:04:54,460 We have our try block which can fail, we have our except block 70 00:04:54,490 --> 00:04:58,720 which deals with any failures that occur, we have our else block 71 00:04:58,780 --> 00:05:03,010 which has the code that needs to be run if there were no issues, 72 00:05:03,370 --> 00:05:07,810 and finally, at the very end no matter if there was an issue or no issue, 73 00:05:08,140 --> 00:05:12,640 we have a block of code which clears our website and password entries. 74 00:05:13,240 --> 00:05:16,660 Now you might've noticed there's a little bit of repetition here with the 75 00:05:16,690 --> 00:05:19,090 writing to file. So if you want to, 76 00:05:19,120 --> 00:05:22,660 you could in fact create a separate method somewhere up here. 77 00:05:23,110 --> 00:05:26,980 But I'm actually going to keep this as it is just because I think when you look 78 00:05:26,980 --> 00:05:30,550 at this code, if you had any issues and you wanted to review it, 79 00:05:31,060 --> 00:05:35,920 this is much easier to understand and reason about compared to a separate 80 00:05:35,920 --> 00:05:36,753 function. 81 00:05:37,330 --> 00:05:40,930 Feel free to refactor this code and make it as short as you want. 82 00:05:41,380 --> 00:05:43,210 But this is the version I'm going to keep 83 00:05:43,450 --> 00:05:46,690 just so that if you had any issues and you want to take a look at it, 84 00:05:46,960 --> 00:05:47,860 it's there for you 85 00:05:47,950 --> 00:05:52,950 and it's easy to see the try, except, else, and finally blocks with all of the 86 00:05:54,070 --> 00:05:55,660 code together in one place. 87 00:05:58,130 --> 00:05:59,330 Now in the next lesson, 88 00:05:59,390 --> 00:06:02,750 we're going to be completing the functionality of our password manager. 89 00:06:03,110 --> 00:06:06,380 We're gonna add that all important search functionality 90 00:06:06,740 --> 00:06:11,510 which is going to look through our JSON, fetch the results for a particular 91 00:06:11,510 --> 00:06:14,630 website, and then show it to us in a popup. 92 00:06:15,050 --> 00:06:18,380 So for all of that and more, I'll see you on the next lesson.