1 00:00:00,350 --> 00:00:08,000 Okay, we have some more code to go. We have defined the view, the search, and the add 2 00:00:08,000 --> 00:00:13,410 buttons, so now we have the delete, the update, and the close button, and I would 3 00:00:13,410 --> 00:00:17,609 like to continue with the delete button because the delete button is easier to 4 00:00:17,609 --> 00:00:29,279 implement than the update button, so let me call the interface again. And again think 5 00:00:29,279 --> 00:00:34,440 about the user, and what will user might expect is they may want to delete 6 00:00:34,440 --> 00:00:39,930 one of the rows. Let's say this row. So they expect to select this row, 7 00:00:39,930 --> 00:00:43,530 and then they press the delete selected button 8 00:00:43,530 --> 00:00:49,530 and this row will disappear from the database, and they may also want to when they 9 00:00:49,530 --> 00:00:56,460 select row they may also want to see the data in these entries. And we will 10 00:00:56,460 --> 00:01:00,510 take care of that too, so we will fill these entries with the corresponding 11 00:01:00,510 --> 00:01:06,510 values when the user clicks one of the rows here. Alright, that makes sense I 12 00:01:06,510 --> 00:01:14,430 believe. And now let's look at the delete function in the backend script, so what 13 00:01:14,430 --> 00:01:21,210 delete does is it expects for an ID, the ID of the row, and then this SQL 14 00:01:21,210 --> 00:01:27,479 statement then looks for this ID and deletes the entire row of the book table 15 00:01:27,479 --> 00:01:35,159 where the ID is equal to this given ID here, so what we need to do is when the 16 00:01:35,159 --> 00:01:40,170 user selects one of the rows in the list box, we need to grab the ID of that 17 00:01:40,170 --> 00:01:46,820 row and then that send back ID to the delete function over the backend script. 18 00:01:46,820 --> 00:01:55,350 And then the delete function takes care of the row. Oh good, and again in this 19 00:01:55,350 --> 00:02:01,340 case you do also want to append some sort of delete command function to the, 20 00:02:01,340 --> 00:02:06,840 here, to the delete button, but in this case I would actually like to do 21 00:02:06,840 --> 00:02:12,569 a button-up approach, so let's first think of how we're going to get the row 22 00:02:12,569 --> 00:02:19,469 selected by the user. So let's think about that first, and you 23 00:02:19,469 --> 00:02:24,739 don't know probably, but there is a method called bind of the tkinter library and 24 00:02:24,739 --> 00:02:32,730 bind is used to bind a function to a widget event. So let me write the bind 25 00:02:32,730 --> 00:02:36,810 method, so that you understand things better, so we all we are binding a method 26 00:02:36,810 --> 00:02:43,409 here to the list box widget, so it makes sense to write that method after way we 27 00:02:43,409 --> 00:02:50,099 have defined the list widget, so we define this widget here and we configure 28 00:02:50,099 --> 00:02:57,060 it and then list1 dot bind and the bind method that takes two arguments. 29 00:02:57,060 --> 00:03:01,799 So it takes the event type and also it takes the function that you want 30 00:03:01,799 --> 00:03:08,909 to bind to the event type. And the event type here actually goes inside these 31 00:03:08,909 --> 00:03:18,540 characters and it's called ListboxSelect. And then you want to specify a function 32 00:03:18,540 --> 00:03:24,780 here that returns a list object with the selection, so something like this. 33 00:03:24,780 --> 00:03:32,479 Actually we will expect a tuple in this case, a tuple with the ID, the title, 34 00:03:32,479 --> 00:03:39,349 the author, and the year, and the ISBN number, so let's call that function 35 00:03:39,349 --> 00:03:50,790 get selected row. Okay, and then we go ahead and define that function. 36 00:03:50,790 --> 00:03:59,489 Let's define it in the very beginning here. So def get selected row and this function now 37 00:03:59,489 --> 00:04:04,859 because we have bind it to an event, to a widget event, this function gets 38 00:04:04,859 --> 00:04:09,449 a special parameter called event, and the event parameter holds the information 39 00:04:09,449 --> 00:04:16,470 about the type of the event. So Python knows that when you pass these 40 00:04:16,470 --> 00:04:25,380 to the bind method it expects the function to have this event parameter. 41 00:04:25,380 --> 00:04:30,750 Then, so again this function will return the tuple, the selected tuple, but first of 42 00:04:30,750 --> 00:04:36,390 all the way this works is that we first need to get the index of the list 43 00:04:36,390 --> 00:04:41,460 from the list box. You know the list may have let's say 10 rows and the first row 44 00:04:41,460 --> 00:04:48,570 will have an index of 0, the second an index of 1 and so on up to 9 if we have 10 rows. 45 00:04:48,570 --> 00:04:56,850 So to get the index of the selected row of the list box we refer to the listbox, 46 00:04:56,850 --> 00:05:05,040 and then to the cur selection method of the list box, all right, and I 47 00:05:05,040 --> 00:05:11,490 would actually like to just make a a temporary return of the index here so that 48 00:05:11,490 --> 00:05:18,350 you see what this object is, and how it looks like. So let's hope this will work! 49 00:05:18,350 --> 00:05:28,220 It should work. Python frontend, yeah and so view all. 50 00:05:28,220 --> 00:05:34,440 Actually we should have printed out the index here. We are just returning it, 51 00:05:34,440 --> 00:05:45,440 so print index and let's try this out again. So I expect to print other index here. 52 00:05:45,440 --> 00:05:54,560 Yeah, so this is the index of the selected row, so this is row 1, sorry 0 53 00:05:54,560 --> 00:06:04,919 with index 0, 1, 2 and so on. However as you see this is not a plain normal, this is 54 00:06:04,919 --> 00:06:11,400 actually a tuple, a tuple with one item. So what we need to do is a very simple 55 00:06:11,400 --> 00:06:18,810 trick, and we just grab the item with index 0 of the tuple which is number 2 56 00:06:18,810 --> 00:06:22,400 in this case, 0 in this case, and so on and then we 57 00:06:22,400 --> 00:06:32,319 might try this again. View all. And now we get single numbers. Great, so 58 00:06:32,319 --> 00:06:36,819 we're very close but not there yet because we need to get the actual tuple 59 00:06:36,819 --> 00:06:42,219 with all the values of the row and to get that you need to apply another 60 00:06:42,219 --> 00:06:49,659 method called get, so let's say a selected tuple, so the actual tuple 61 00:06:49,659 --> 00:06:55,270 that we want, the actual row that we want is equal to list1 dot get 62 00:06:55,270 --> 00:07:03,009 index, so you can read it like this. From the listbox get the tuple 63 00:07:03,009 --> 00:07:14,909 with index x and then we can try this out so what are we getting here? 64 00:07:14,909 --> 00:07:21,310 Don't get confused with this row, this is being printed out because in the 65 00:07:21,310 --> 00:07:27,129 backend script we actually have a search function being printed out, so this is 66 00:07:27,129 --> 00:07:31,659 printing the output of the search function, so this function is saying give 67 00:07:31,659 --> 00:07:38,680 me the row with John Smith as author name, and next time this will not be 68 00:07:38,680 --> 00:07:47,770 executed, so back. What we want to do is select a row and we get the row printed 69 00:07:47,770 --> 00:07:57,310 out there as a tuple, so that is great. So what's next? Well next is we need to pass 70 00:07:57,310 --> 00:08:04,409 the ID of the selected tuple to the delete function of the backend script. 71 00:08:04,409 --> 00:08:17,949 we go to the delete selected button. Command equals delete command. That's how 72 00:08:17,949 --> 00:08:27,940 I'm gonna call the script, and that should be oh here. Def delete command. 73 00:08:27,940 --> 00:08:39,310 And what we have here is backend dot delete, and again the delete method gets 74 00:08:39,310 --> 00:08:47,050 as argument the ID, so we have a tuple called get selected row, so we need to 75 00:08:47,050 --> 00:08:53,770 return, return the selected tuple so if we call the function now get selected row. 76 00:08:53,770 --> 00:09:06,270 Selected row, and we need the item with index 0 from the get selected row. 77 00:09:06,270 --> 00:09:17,500 So save the script. And we got an error at line 24. I don't have the colon here. 78 00:09:17,500 --> 00:09:29,830 Try out again. View and let's try to delete "The Moon", delete and Python is saying that 79 00:09:29,830 --> 00:09:35,260 get selected row is missing one required positional argument and that's 80 00:09:35,260 --> 00:09:43,360 the event argument, and so python is right because here we have an event parameter, 81 00:09:43,360 --> 00:09:49,150 so we need to pass that as an argument. But here we are calling the function 82 00:09:49,150 --> 00:09:54,640 without any argument, so we're getting an error, on the other and we cannot remove 83 00:09:54,640 --> 00:10:03,040 this event because this function is also being executed by the bind method so in 84 00:10:03,040 --> 00:10:09,550 that case the hero of the day here would be a global variable, so you might 85 00:10:09,550 --> 00:10:14,620 already know that local variables like the selected tuple is a local 86 00:10:14,620 --> 00:10:21,570 variable because it's defined inside a function, so if you print this tuple 87 00:10:21,570 --> 00:10:27,850 outside the function select a tuple, you'll get an error because Python will say 88 00:10:27,850 --> 00:10:34,180 sorry I don't recognize this. This is an undefined object because local variables 89 00:10:34,180 --> 00:10:40,730 make sense only inside the function, so in that case we can use global variables, 90 00:10:40,730 --> 00:10:47,740 and the way to create a global variable is by using the global keyword and then 91 00:10:47,980 --> 00:10:54,560 declaring the name of the variable that you want to create, so in that case if 92 00:10:54,560 --> 00:10:59,870 you print out the selected tuple outside the function, you'll get the value of the 93 00:10:59,870 --> 00:11:05,170 selected tuple, and the value of the selected tuple in this case it would be 94 00:11:05,170 --> 00:11:12,139 the tuple with the values of the row. So in that case we don't need to return the 95 00:11:12,139 --> 00:11:16,970 selected tuple because we can simply point to the selected tuple variable in 96 00:11:16,970 --> 00:11:25,579 that case, and we need to fix our delete function here. So we want selected tuple. 97 00:11:25,579 --> 00:11:34,670 And we want the item with index 0 from the selected tuple, so let's execute again. 98 00:11:34,670 --> 00:11:46,490 View all and let's delete "The Moon". Delete selected, view all and "The Moon" 99 00:11:46,490 --> 00:11:55,310 is gone, so it seems to be working. Now I'd also want to fill the entries 100 00:11:55,310 --> 00:12:03,410 with a selected tuple or row if you like. So we need to use the insert function 101 00:12:03,410 --> 00:12:09,410 of the entry widget, and we could actually write those methods inside the get selected 102 00:12:09,410 --> 00:12:14,660 row function because you know when the user clicks one of the rows, when they 103 00:12:14,660 --> 00:12:19,040 select one of the rows we immediately want to fill those entries with values. 104 00:12:19,040 --> 00:12:24,500 And the first would be the title and we want to make sure the entry is 105 00:12:24,500 --> 00:12:29,810 empty, so delete 0 to end, delete everything from the entry if there is 106 00:12:29,810 --> 00:12:39,620 something, and then e1 insert. So what we want to insert in the author entry? 107 00:12:39,620 --> 00:12:50,000 Well that would be the selected tuple with the index of 1, so the ID has an index 108 00:12:50,000 --> 00:12:59,480 of 0, the title has an index of 1. And this would be the same for the other 109 00:12:59,480 --> 00:13:15,860 entries as well, so we have e1, e2, e3, and e4. And then here we want to grab the author name. 110 00:13:15,860 --> 00:13:26,060 Here we want the year, and the ISBN number in here. Great, so I hope this 111 00:13:26,060 --> 00:13:32,840 will work. It should work, so view all select something and insert method 112 00:13:32,840 --> 00:13:39,530 is missing one required argument. I think I forgot to put where I want to 113 00:13:39,530 --> 00:13:56,990 insert the new values, so we need to end here, here, here and here. So let's see 114 00:13:56,990 --> 00:14:06,620 again. View all, and now it seems to be working, so "Trees and Grass", Ben Sand 115 00:14:06,620 --> 00:14:15,910 and so on, and let me try to delete this. Delete, view all, and the entry is gone. 116 00:14:15,910 --> 00:14:22,400 Great, so now let's go ahead without wasting any time. Let's go ahead and implement 117 00:14:22,400 --> 00:14:28,220 the update function so back to our backend script. The update function gets an ID, 118 00:14:28,220 --> 00:14:34,880 and title, author, year, and ISBN. So unlike the delete function which only 119 00:14:34,880 --> 00:14:43,850 got one item. This gets four items, five items actually, so in the delete command 120 00:14:43,850 --> 00:14:51,080 function we pass the selected tuple with an index of 0. Now the update 121 00:14:51,080 --> 00:14:59,540 function will be similar, similar structure but then we will have multiple 122 00:14:59,540 --> 00:15:06,590 arguments here, so we have ID title, author, year and ISBN, so selected tuple 123 00:15:06,590 --> 00:15:14,960 with an index of one. Selected tuple with an index of two. Selected tuple with an 124 00:15:14,960 --> 00:15:27,650 index of three, and selected tuple with an index of 4, and then we need to add 125 00:15:27,650 --> 00:15:42,200 that function to the update button. So update command, alright, and I forgot to 126 00:15:42,200 --> 00:15:55,279 change this. Update command. This should work, so let's see. I've forgotten to pass 127 00:15:55,279 --> 00:16:07,010 the name of the parameter here. So command equals update command, save and 128 00:16:07,010 --> 00:16:20,050 execute again and view all. Let's try to update this row, so let's say nine, and 129 00:16:20,050 --> 00:16:28,640 you press update selected and yet another error. Don't get scared about 130 00:16:28,640 --> 00:16:32,930 errors, the more errors you see, the more familiar you will become with Python. 131 00:16:32,930 --> 00:16:39,650 It's important to focus on the error to see what line you're getting the error and try 132 00:16:39,650 --> 00:16:43,850 to understand what type of the error, and the message you're getting. So in this case 133 00:16:43,850 --> 00:16:49,790 this say delete takes one positional argument, but five were given. 134 00:16:49,790 --> 00:16:54,980 We didn't execute a delete function here. we executed the update button which gets 135 00:16:54,980 --> 00:17:05,050 an update command function, and you go to the update command, so the update command. 136 00:17:05,050 --> 00:17:10,880 Backend delete. That's why we are getting this error, the update command 137 00:17:10,880 --> 00:17:16,250 is actually executing the delete method of the backend script, so we want 138 00:17:16,250 --> 00:17:20,110 update instead of delete. And save the script and execute again. 139 00:17:26,600 --> 00:17:36,809 View all. I want to really update this number here, so 9 update selected, view all. 140 00:17:36,809 --> 00:17:44,159 And it's not working, and in this case we're not even getting an error here so 141 00:17:44,159 --> 00:17:52,919 you may feel lost at the moment, so what you could do in this case is check what you 142 00:17:52,919 --> 00:18:01,519 are returning in your update command function, so you know that you can 143 00:18:01,519 --> 00:18:06,450 isolate problems by using print statements, so let's say you want to 144 00:18:06,450 --> 00:18:12,690 check what you are sending to the update function. I know the problem here, 145 00:18:12,690 --> 00:18:19,940 but just to show you the way you can troubleshoot things, so print out and 146 00:18:19,940 --> 00:18:28,470 execute this again. View all, get this "Grasslands", update selected and you 147 00:18:28,470 --> 00:18:36,389 see that the tuple is being printed out as it is, so this number is not changing. 148 00:18:36,389 --> 00:18:42,799 Actually I didn't change it, so let me change this again. Let's say 24 and 149 00:18:42,799 --> 00:18:49,019 update selected and so you see that the number 24 is not being printed out here, 150 00:18:49,019 --> 00:18:55,289 so that means we are sending to the database this record again, so we're not 151 00:18:55,289 --> 00:19:01,080 sending the updated record. So why is that? If you have already found it from 152 00:19:01,080 --> 00:19:05,450 earlier when I have an arrow this function, that's very great. 153 00:19:05,450 --> 00:19:12,029 If you haven't well the reason is that we are sending to the update method the 154 00:19:12,029 --> 00:19:17,519 selected tuple, and the selected tuple is the one that the user has selected, 155 00:19:17,519 --> 00:19:22,980 so it's not the actual entry that the user is sending to the update command, 156 00:19:22,980 --> 00:19:30,389 so in that case we actually want to send out these values, so the current values 157 00:19:30,389 --> 00:19:37,830 of the entries, so I'll copy this and paste it just here. 158 00:19:37,830 --> 00:19:44,820 Okay, and the first selected tuple is the ID, so we want to keep the ID of 159 00:19:44,820 --> 00:19:52,230 the selected row because the user is changing the other values, not the ID. 160 00:19:52,230 --> 00:20:03,970 And this looks fine, The bracket closes here. Save so delete this one, 161 00:20:03,970 --> 00:20:11,669 save, execute again. View all, go to this and let's say 3. 162 00:20:11,669 --> 00:20:20,740 Update selected, view all and 3 is there. Delete, view all, it goes away. 163 00:20:20,740 --> 00:20:27,279 You can add it again because you have it in your entries. Add entry and it was added 164 00:20:27,279 --> 00:20:35,409 again and you can see it here. So everything is working great, and we 165 00:20:35,409 --> 00:20:39,460 want to close this program but the close button is not working at the moment, 166 00:20:39,460 --> 00:20:45,490 so let's go ahead and implement that as well, and that's very 167 00:20:45,490 --> 00:20:53,590 straightforward, you just go here and command equals to. So you want to destroy 168 00:20:53,590 --> 00:20:59,490 the window, right? So window dot destroy. That's it. 169 00:20:59,490 --> 00:21:08,500 Save the script, try it out. So all these are working as usual. Close and the 170 00:21:08,500 --> 00:21:16,720 window closes, and you may also want to put a title to your window, and you use the 171 00:21:16,720 --> 00:21:23,639 WM title method of the window object. Title and let's say 172 00:21:25,330 --> 00:21:37,120 book store, and you should see that name in the title bar, so finally 173 00:21:37,120 --> 00:21:42,129 we are done with this program, and I know there might be things to improve and 174 00:21:42,129 --> 00:21:47,700 I would welcome any suggestions from you so that we could improve the program. 175 00:21:47,700 --> 00:21:53,980 Programs have versions, so this is version zero you could say, and I hope you 176 00:21:53,980 --> 00:21:58,200 found this very useful and learned a lot from this, so I'll talk to you later.