WEBVTT 0 00:00.200 --> 00:07.190 Now that we've seen lists as well as dictionaries, I want to talk about a concept that you often see 1 00:07.190 --> 00:11.690 in both of these collection types, and that's something called nesting. 2 00:12.080 --> 00:19.280 Now, if we imagine a list or a dictionary being something like a folder where lots of things can be 3 00:19.280 --> 00:26.600 stored inside it, then nesting lists and dictionaries is just a matter of putting one inside the other. 4 00:27.260 --> 00:31.300 For example, here's a dictionary that is very simple. 5 00:31.300 --> 00:33.640 It's only got one key / value pair. 6 00:33.850 --> 00:41.140 Now we know that we can add multiple key value pairs into the same dictionary by just adding a bunch 7 00:41.140 --> 00:43.000 of commas to separate them. 8 00:43.570 --> 00:52.840 Now what if instead of having a simple value like a string or a number, I could also put a list as 9 00:52.840 --> 00:54.520 a value as well. 10 00:54.910 --> 00:59.800 Similarly, I could also use a dictionary as a value. 11 01:00.040 --> 01:04.690 In this case, we've got a list as the value for key, 12 01:04.720 --> 01:10.330 this first one, and we've got a dictionary as the value for key2. 13 01:10.720 --> 01:17.770 Notice how this is a list and a dictionary nested inside another dictionary. 14 01:17.800 --> 01:24.120 The structure gets a little bit more complex, but it gives us more flexibility when we're trying to 15 01:24.120 --> 01:26.940 store more complex pieces of data. 16 01:27.840 --> 01:34.020 Coming back to our code, let's go ahead and create some sample dictionaries to see what this actually 17 01:34.020 --> 01:35.640 looks like in real life. 18 01:35.640 --> 01:43.820 For example, this could be a dictionary that contains the country as the key and the city that is the 19 01:43.820 --> 01:46.040 capital as the value. 20 01:46.220 --> 01:50.120 So for France, that's Paris, for Germany, that's Berlin. 21 01:50.150 --> 01:53.720 This is a very simple dictionary that you've seen already. 22 01:53.750 --> 02:02.900 Now, if I wanted to nest a list in a dictionary, then I would be able to represent even more complex 23 02:02.900 --> 02:03.620 data. 24 02:03.620 --> 02:12.020 For example, if I had a travel_log where I was going to collect a dictionary of all the cities I had 25 02:12.020 --> 02:14.510 been for each of the countries I've traveled to. 26 02:14.510 --> 02:22.250 So, for example, if I had traveled to France and I wanted to say that I've been to multiple cities, 27 02:22.250 --> 02:28.040 I can't simply just say, Paris, and then Lille, Dijon, 28 02:28.550 --> 02:34.000 that doesn't really work, because each key can only have one value. 29 02:34.030 --> 02:40.690 The only way that we can make these three pieces of data, one value, is by turning it into a list 30 02:40.690 --> 02:41.680 like so. 31 02:41.770 --> 02:51.100 So now in our travel_log dictionary, as represented by the curly braces, we have one key/value pair. 32 02:51.220 --> 02:56.040 And it just so happens that the value in this case is a list. 33 02:56.520 --> 03:01.740 And of course, you can go on and add as many entries as you would like, 34 03:01.740 --> 03:08.670 and still preserving this kind of structure of key being a string and the value being a list. 35 03:09.360 --> 03:16.770 Now I've got a challenge for you to test your understanding of how lists nested inside dictionaries 36 03:16.770 --> 03:17.760 might work. 37 03:17.790 --> 03:27.990 I want you to guess and figure out how can you print out the Lille string from this travel_log. 38 03:28.020 --> 03:36.510 So think about how you might access items in a dictionary, and then think about how you access items 39 03:36.510 --> 03:38.010 in a list. 40 03:38.010 --> 03:41.880 And the goal is just to print out this Lille. 41 03:41.910 --> 03:43.020 Pause the video. 42 03:43.020 --> 03:43.980 Give this a go. 43 03:45.770 --> 03:50.870 Okay, so let's first start with accessing this list. 44 03:50.870 --> 03:58.910 So if we go ahead and use our print statement to tap into the travel_log, we know that we can access 45 03:58.910 --> 04:04.040 the value of a dictionary by using the key. 46 04:04.040 --> 04:06.380 So we use the square brackets. 47 04:06.380 --> 04:10.930 And then we have to type the key which in this case is France. 48 04:10.930 --> 04:15.400 So if we print this right now we're getting hold of the list. 49 04:15.400 --> 04:17.740 And we know how to work with lists already. 50 04:17.740 --> 04:26.800 So if we want the item at index zero one then we just need another set of square brackets and add one 51 04:26.800 --> 04:27.670 in there. 52 04:27.670 --> 04:33.640 So now if we run this you can see we're able to get hold of this item. 53 04:33.940 --> 04:42.520 Now, we've previously seen that you can nest lists inside other lists, and you can end up with a many 54 04:42.520 --> 04:44.140 layered nested list. 55 04:44.140 --> 04:52.810 So for example, if I had a list that had the letters A and B, I can nest a list inside there at the 56 04:52.810 --> 04:54.160 index[2], 57 04:54.190 --> 04:56.080 So, 0 1 2. 58 04:56.110 --> 04:59.880 The third item in this list is another list. 59 04:59.880 --> 05:03.180 And I'm going to add C and D. 60 05:03.360 --> 05:06.540 So now we have what's called a 2D list, 61 05:06.540 --> 05:07.800 we have a list, 62 05:07.800 --> 05:10.620 and then we have a list inside that list. 63 05:10.620 --> 05:13.230 So here's another challenge for you. 64 05:13.260 --> 05:18.840 See if you can figure out how to print out this letter D from the nested list. 65 05:18.840 --> 05:24.420 Think about what we did before and think about what you've learned previously about nested lists, 66 05:24.450 --> 05:27.450 to complete this challenge. Pause the video now. 67 05:30.210 --> 05:34.530 Okay, so let's first access this list. 68 05:34.530 --> 05:41.790 So if we go ahead and print our nested list and then we put in the index of this list, it would be 69 05:41.790 --> 05:44.610 at 0, 1, 2. 70 05:44.640 --> 05:48.320 So let's put two inside the set of square brackets. 71 05:48.320 --> 05:50.960 I'm just going to comment this other print statement out. 72 05:50.960 --> 05:53.960 And now you can see we've got hold of C and D. 73 05:54.110 --> 06:00.650 So now that we've got that list how would we access D if we were working with this list. 74 06:00.650 --> 06:05.540 Well we would tap into the item at index 1. 75 06:05.540 --> 06:11.120 So what we know is this part of the code results in this list. 76 06:11.120 --> 06:17.770 Then to get hold of D, all we need to do is add another set of square brackets and then add 1 as 77 06:17.770 --> 06:18.610 the index. 78 06:18.610 --> 06:23.470 And now when I print it, I'm able to get hold of that item D. 79 06:23.470 --> 06:31.360 Now this is quite confusing at first because there's a lot of nesting, and it can be a little bit difficult 80 06:31.360 --> 06:32.980 to wrap your head around it, 81 06:32.980 --> 06:40.690 but if you try it a few times with some of the other items in the nested list inside a dictionary, or 82 06:40.690 --> 06:48.100 the nested list inside a list, then eventually it will make sense and it's not actually so complicated. 83 06:48.460 --> 06:55.120 Now, other things that you can nest is you can actually nest a dictionary within a dictionary itself. 84 06:55.150 --> 07:03.660 So if I have this travel_log and I'm going to copy it, and then comment it out so that I can have a different 85 07:03.660 --> 07:12.480 version of it. Now if I wanted to, instead of storing a list as the value of the key, 86 07:12.510 --> 07:16.410 France, I can also store a dictionary. 87 07:16.410 --> 07:25.100 So now this is a dictionary which has a key of France, and the value for that key happens to be another 88 07:25.100 --> 07:25.910 dictionary. 89 07:25.910 --> 07:28.340 So what's going to go inside this dictionary? 90 07:28.340 --> 07:33.500 Well, if I was really building a travel_log, I might want to log. 91 07:33.500 --> 07:36.230 Well, how many times have I visited this country. 92 07:36.230 --> 07:46.940 So let's create a "num_times_visited" key for this France and make sure that we've got it as a string. 93 07:46.940 --> 07:49.640 And then for the value we could have a number. 94 07:49.640 --> 07:58.580 So let's say I've been to France 8 times, then that would be the first key / value pair in our France, 95 07:58.760 --> 08:00.260 entry. 96 08:00.260 --> 08:06.380 And then we've also got another key called cities_visited. 97 08:07.400 --> 08:16.570 And now what we can do is we can save the list into the value for that key. 98 08:16.600 --> 08:26.500 So now we've got a list nested inside a dictionary which is nested inside another dictionary. 99 08:26.500 --> 08:31.990 And if I was to complete my travel_log then it might look something like this. 100 08:31.990 --> 08:35.500 And you can see that our data is more complex. 101 08:35.500 --> 08:43.890 We've got more key/value pairs associated, and we've essentially got a much better way of organizing 102 08:43.890 --> 08:45.840 the data for our travel_log. 103 08:45.870 --> 08:52.260 So now comes the question of how would you access some of the items from this more complex travel_log? 104 08:52.260 --> 08:58.050 Can you figure out how to print out Stuttgart from this travel_log? 105 08:58.050 --> 09:04.860 Figure out how you might access this dictionary and then how you might access this list, and then how 106 09:04.860 --> 09:08.640 you might access this item in the list so that you can print it out. 107 09:08.670 --> 09:10.080 Pause the video now. 108 09:14.040 --> 09:14.520 All right. 109 09:14.520 --> 09:16.350 So let's go step by step. 110 09:16.350 --> 09:22.170 The first step going inside this dictionary is we have a key and we have a value. 111 09:22.170 --> 09:24.540 So let's try and pick out this value. 112 09:24.570 --> 09:32.060 We can do that by printing out the travel_log and then using square brackets to tap into Germany. 113 09:32.450 --> 09:40.610 Now when we print this line, we should be able to get this dictionary that contains all of this data. 114 09:40.610 --> 09:46.490 So to narrow it down to this list we have to again use the next key. 115 09:46.490 --> 09:53.590 So add a set of square brackets and then use cities_visited and making sure that you've actually typed 116 09:53.590 --> 09:55.660 it right without any typos. 117 09:55.690 --> 10:02.830 Often it's easier to just copy and paste, and now I should be able to get the list that's stored under 118 10:02.830 --> 10:03.730 that key. 119 10:03.760 --> 10:09.880 So finally, to access this item in the list, it's at index 012. 120 10:09.910 --> 10:12.310 So another set of square brackets, 121 10:12.310 --> 10:14.110 put the index 2 in there. 122 10:14.110 --> 10:17.230 And we've got Stuttgart being printed out here. 123 10:17.410 --> 10:18.910 So there you have it. 124 10:18.910 --> 10:25.390 You have lists inside dictionaries, dictionaries inside dictionaries, lists, inside lists, and a 125 10:25.390 --> 10:31.660 whole lot of different ways of organizing your data and working with dictionaries in Python. 126 10:31.810 --> 10:38.410 Next, we've got a quiz for you to test some of your knowledge on these dictionaries, and hopefully 127 10:38.410 --> 10:40.630 you will pass with flying colors.