1 00:00:05,200 --> 00:00:09,280 Alright, so we've seen how to add and remove items in a dictionary. Now we'll use those 2 00:00:09,280 --> 00:00:14,560 techniques in our menu program. We'll be working in buy_computer_dict once more. 3 00:00:15,192 --> 00:00:19,760 What I'm going to do now is start by defining an empty dictionary, just like we did with the 4 00:00:19,760 --> 00:00:25,096 empty list in the earlier version of this code. Alright, so I'm going to come up here, and below 5 00:00:25,096 --> 00:00:31,479 the current_choice, line 9, we're going to type computer_parts 6 00:00:31,479 --> 00:00:38,333 equals, and left and right curly braces. A comment there - create an empty dictionary. 7 00:00:41,200 --> 00:00:44,800 Alright, so creating an empty dictionary is very similar to creating an empty list, 8 00:00:44,800 --> 00:00:51,600 but this time we're using curly braces instead of square brackets. I'll just add another space there. 9 00:00:51,600 --> 00:00:55,200 See it wants two spaces before the inline comment. We'll just do a tab. 10 00:00:55,200 --> 00:01:00,195 So inside our loop, we'll check if the chosen part is already in this new dictionary. If it is, 11 00:01:00,195 --> 00:01:07,040 we'll remove it - otherwise, we'll add it. We're going to go down here to under chosen_part, 12 00:01:07,040 --> 00:01:15,299 and basically, I'm adding some code here on line 15: if current_choice is in computer_paths colon, 13 00:01:16,250 --> 00:01:22,620 and a note there for us as a comment - it's already in, so remove it. 14 00:01:24,160 --> 00:01:31,116 And we'll do a print parentheses, using an f-string, so f then double quotes, Removing, then left and right 15 00:01:31,116 --> 00:01:36,055 curly braces, chosen_part in those curly braces, and ending the line. 16 00:01:36,960 --> 00:01:41,486 Then the actual code would be computer_parts.pop 17 00:01:41,486 --> 00:01:45,590 parentheses, and it will be current_choice. 18 00:01:48,880 --> 00:01:55,440 Otherwise, we're going to add an else here now, and the else - well we'll indent this code now because it's 19 00:01:55,440 --> 00:01:59,680 correctly saying that it's printing, it's, sorry, it's adding the chosen part and that was the 20 00:01:59,680 --> 00:02:04,320 code that was there previously. We're back on that shortly. But in terms of what we've added already, 21 00:02:04,320 --> 00:02:09,520 we've now added the code from line 15 onwards, to remove an entry from the dictionary, and you can 22 00:02:09,520 --> 00:02:13,760 see that it's very similar to the code we used to remove an item from the list - just that we're using 23 00:02:13,760 --> 00:02:19,660 pop instead of remove on line 18. Getting back to adding a new entry to the dictionary, 24 00:02:19,660 --> 00:02:25,280 all we need to do is assign the value to the dictionary key, and we'll leave our print in that we've got on line 20. 25 00:02:25,280 --> 00:02:29,280 And on line 21, I'm going to do computer_parts 26 00:02:29,280 --> 00:02:33,251 left square bracket, and within those brackets, current_choice 27 00:02:33,251 --> 00:02:36,960 is equal to, outside of the square bracket, chosen_part. 28 00:02:39,360 --> 00:02:44,480 So line 21, we use the key that's stored in current_choice. Remember, 29 00:02:44,480 --> 00:02:49,680 that will be one of the characters that's a key in the available_parts dictionary. 30 00:02:49,680 --> 00:02:54,160 On line 13, if we go up there and have a look, we check if the user's input 31 00:02:54,160 --> 00:02:59,200 is in available_parts. By the time we get to line 21, 32 00:02:59,200 --> 00:03:02,960 we know that current_choice must be one of the characters from 1 through 6. 33 00:03:03,760 --> 00:03:08,240 If you're a bit unsure about that, run the program in the debugger, to see what line 21 is doing. 34 00:03:09,200 --> 00:03:14,720 Firstly, though, it'll be helpful to print out the dictionary, so let's do that. That'll be outside 35 00:03:14,720 --> 00:03:20,240 of the else block, at the same level as our if and else above. So what we're going to do there, 36 00:03:20,240 --> 00:03:29,760 is type print parentheses f double quotes Your dictionary now contains, colon, then in 37 00:03:29,760 --> 00:03:35,276 left and right curly braces, computer_parts. Alright, so let's run this code now. 38 00:03:37,840 --> 00:03:43,317 So what I'm going to do is start. I've got the menu printed. I'm going to choose a monitor, number 2. 39 00:03:44,880 --> 00:03:48,160 Move this back a little bit so we can see - Your dictionary now contains 40 00:03:48,160 --> 00:03:54,160 2 monitor, which is correct. So that caused lines 20 and 21 to be executed - you can see there from 41 00:03:54,160 --> 00:03:59,760 the text. Specifically, we got the text adding monitor, then on the next line, monitor was added 42 00:03:59,760 --> 00:04:05,587 to the dictionary with the key 2. Well let's try again. This time, I'll add option 1, computer - 43 00:04:06,320 --> 00:04:12,080 Adding computer, Your dictionary now contains 2 monitor, and we've got our computer there as option 1, 44 00:04:12,080 --> 00:04:16,959 as the key as well. So now we'll try removing something. I'm going to enter 2 to remove the monitor - 45 00:04:16,959 --> 00:04:20,720 Removing monitor, Your dictionary now contains only the computer, and you can see that is the 46 00:04:20,720 --> 00:04:25,920 case there, on screen. Remember that we should always test boundary conditions. 47 00:04:25,920 --> 00:04:31,680 So here, one boundary condition would be removing the last item to leave an empty dictionary. 48 00:04:31,680 --> 00:04:37,002 So let's enter 1 here now, to remove the computer, and that's going to leave the dictionary empty. 49 00:04:37,002 --> 00:04:41,360 And you can see that still works. Experiment to make sure all the options work, 50 00:04:41,360 --> 00:04:47,760 and that invalid options cause the menu to be printed again. Enter zero to quit, when you've finished testing. 51 00:04:47,760 --> 00:04:53,360 Alright, so in the next few videos, we'll look at linking dictionaries together. When dictionaries 52 00:04:53,360 --> 00:04:58,960 work together, or with lists, you can produce some very useful code. See you in the next video.