1 00:00:01,080 --> 00:00:02,580 Hi, guys and welcome back. 2 00:00:02,580 --> 00:00:05,690 In this video, we're going to learn about lists, tuples, 3 00:00:05,690 --> 00:00:09,610 and sets. Three different collections in Python that 4 00:00:09,610 --> 00:00:13,470 allows us to store multiple values in a single variable. 5 00:00:13,470 --> 00:00:15,090 So that we can use them all at once 6 00:00:15,090 --> 00:00:17,383 or maybe extract some of them individually. 7 00:00:18,550 --> 00:00:19,970 Let's get started. 8 00:00:19,970 --> 00:00:22,370 We're going to define one of each just so you 9 00:00:22,370 --> 00:00:24,780 know how they are defined. 10 00:00:24,780 --> 00:00:29,493 So, l is going to be a list of three elements. 11 00:00:31,290 --> 00:00:34,620 And here I've created a variable called l for lists 12 00:00:34,620 --> 00:00:36,720 and I've made it equal to a list. 13 00:00:36,720 --> 00:00:40,340 The list is defined by using square brackets 14 00:00:40,340 --> 00:00:42,830 and inside the square brackets you can put different 15 00:00:42,830 --> 00:00:46,150 values as long as they are separated by a comma. 16 00:00:46,150 --> 00:00:49,630 So what I've got here is one string, then I've got a comma, 17 00:00:49,630 --> 00:00:51,990 then I've got another string, then I've got another comma, 18 00:00:51,990 --> 00:00:54,820 and then I've got another string. So three strings separated 19 00:00:54,820 --> 00:00:58,703 by commas inside square brackets. This defines a list. 20 00:00:59,620 --> 00:01:02,680 If you didn't have lists or tuples or sets, 21 00:01:02,680 --> 00:01:04,720 you would have to define three variables, 22 00:01:04,720 --> 00:01:06,010 one for each friend. 23 00:01:06,010 --> 00:01:07,780 And that would make it difficult to interact 24 00:01:07,780 --> 00:01:09,360 with all the values at once. 25 00:01:09,360 --> 00:01:10,640 You'll understand what I mean 26 00:01:10,640 --> 00:01:12,633 as we progress through the video. 27 00:01:14,120 --> 00:01:18,640 A tuple is very similar to a list but instead of using 28 00:01:18,640 --> 00:01:21,750 square brackets you use normal brackets. 29 00:01:21,750 --> 00:01:24,370 The key difference between lists and tuples is that 30 00:01:24,370 --> 00:01:28,470 you can't modify a tuple, whereas you can add and remove 31 00:01:28,470 --> 00:01:31,300 elements from a list, you can't add and remove 32 00:01:31,300 --> 00:01:32,480 elements from a tuple. 33 00:01:32,480 --> 00:01:35,040 That's the key difference between the two. 34 00:01:35,040 --> 00:01:39,390 Finally, a set is, again very similar, but you use curly 35 00:01:39,390 --> 00:01:42,703 braces instead of square or normal brackets. 36 00:01:45,490 --> 00:01:48,230 And the key difference between a set and the other two 37 00:01:48,230 --> 00:01:50,460 is that while you can add and remove elements from 38 00:01:50,460 --> 00:01:53,440 a set you can't have duplicate elements. 39 00:01:53,440 --> 00:01:57,070 So you couldn't have Bob twice in the set. 40 00:01:57,070 --> 00:02:01,290 Also, lists and tuples keep the order of the elements. 41 00:02:01,290 --> 00:02:04,220 So whenever you print out this list, it will always have 42 00:02:04,220 --> 00:02:07,120 Bob then Rolf and then Anne in that order, 43 00:02:07,120 --> 00:02:09,800 but sets don't necessarily keep the order, 44 00:02:09,800 --> 00:02:11,500 rather the order is not guaranteed. 45 00:02:11,500 --> 00:02:13,740 So the order could change at any moment. 46 00:02:13,740 --> 00:02:16,920 Sets are useful in a few scenarios that we will learn 47 00:02:16,920 --> 00:02:18,523 about in the coming videos. 48 00:02:19,520 --> 00:02:23,490 You can access individual elements of a list or a tuple 49 00:02:23,490 --> 00:02:25,840 by using subscript notation. 50 00:02:25,840 --> 00:02:27,653 So for example, you can print l. 51 00:02:30,050 --> 00:02:33,060 So what we've got here is our list variable 52 00:02:33,060 --> 00:02:35,487 and then we've got [0]. 53 00:02:37,050 --> 00:02:39,400 This notation here is called subscript notation 54 00:02:39,400 --> 00:02:41,860 and you can apply it to many things in Python 55 00:02:41,860 --> 00:02:43,970 but you can use it on lists and tuples 56 00:02:43,970 --> 00:02:48,823 and what it does is give you that element with index zero. 57 00:02:49,830 --> 00:02:52,890 Elements in programming usually start counting at zero, 58 00:02:52,890 --> 00:02:57,120 so the first element here, Bob has an index of zero. 59 00:02:57,120 --> 00:02:58,700 Then this one has an index of one, 60 00:02:58,700 --> 00:03:00,320 and this one has an index of two. 61 00:03:00,320 --> 00:03:05,120 So you could access Anne by doing l[2]. 62 00:03:05,120 --> 00:03:08,040 This also works for tuples so you can use your tuple 63 00:03:08,040 --> 00:03:11,210 variable there instead and that's totally find as well. 64 00:03:11,210 --> 00:03:14,340 However, it doesn't make sense to do that in sets 65 00:03:14,340 --> 00:03:16,240 because they don't have any order. 66 00:03:16,240 --> 00:03:18,780 So if you access the third element of a set, 67 00:03:18,780 --> 00:03:20,290 you don't know what you're going to get. 68 00:03:20,290 --> 00:03:22,510 That's why sets don't allow you 69 00:03:22,510 --> 00:03:24,313 to use subscript notation on them. 70 00:03:25,520 --> 00:03:28,900 You can modify individual items in a list by accessing 71 00:03:28,900 --> 00:03:31,870 the item itself using subscript notation 72 00:03:31,870 --> 00:03:34,140 and then you treating it like a variable. 73 00:03:34,140 --> 00:03:37,790 So for example, you can say l[0] equals Smith 74 00:03:37,790 --> 00:03:39,900 and then if you print your list and you run it, 75 00:03:39,900 --> 00:03:43,320 you will see that the first element is now Smith, 76 00:03:43,320 --> 00:03:45,470 second one's Rolf and the third one's Anne. 77 00:03:47,020 --> 00:03:51,150 However, if you're trying to modify a tuples element 78 00:03:51,150 --> 00:03:54,510 and you run this file, you will actually get an error 79 00:03:54,510 --> 00:03:58,060 because tuples cannot be modified after they're created 80 00:03:58,060 --> 00:04:01,643 so you can't use the equal sign on anything inside a tuple. 81 00:04:02,700 --> 00:04:04,630 Of course you can not do this on a set 82 00:04:04,630 --> 00:04:07,583 because a set does not allow for this subscript notation. 83 00:04:08,650 --> 00:04:12,900 You can add elements to a list by doing l.append 84 00:04:12,900 --> 00:04:16,480 and what append does is it will add an element 85 00:04:16,480 --> 00:04:17,930 to the end of the list. 86 00:04:17,930 --> 00:04:21,220 So if we append, for example, Smith to this list 87 00:04:21,220 --> 00:04:23,300 and then print it out you'll see that this list 88 00:04:23,300 --> 00:04:25,320 will now have four elements. 89 00:04:25,320 --> 00:04:27,413 That's Bob, Rolf, Anne, and Smith. 90 00:04:28,460 --> 00:04:31,910 But again because tuples to not allow modification, 91 00:04:31,910 --> 00:04:34,440 you can't change them, then if you do something like this 92 00:04:34,440 --> 00:04:36,220 you're also going to get an error and it's going to tell you 93 00:04:36,220 --> 00:04:40,030 that the tuple object has no attribute append. 94 00:04:40,030 --> 00:04:43,410 What that means is that we tried to access something 95 00:04:43,410 --> 00:04:47,257 called append inside, and that's what this full stop means 96 00:04:47,257 --> 00:04:51,170 so we're trying to access append inside of our tuple 97 00:04:51,170 --> 00:04:54,810 but our tuple doesn't have anything called append inside it. 98 00:04:54,810 --> 00:04:57,950 We're going to learn more about what I mean by inside 99 00:04:57,950 --> 00:05:00,460 in the next few videos. It is a little bit 100 00:05:00,460 --> 00:05:03,980 of a more complicated topic but rest assured you can't 101 00:05:03,980 --> 00:05:06,633 add things or remove things from a tuple. 102 00:05:08,160 --> 00:05:12,890 Talking about removal, you can remove things from a list. 103 00:05:12,890 --> 00:05:16,430 We're doing l.remove and then passing in the element 104 00:05:16,430 --> 00:05:17,300 that you want to remove. 105 00:05:17,300 --> 00:05:19,550 For example, if you wanted to remove Bob, 106 00:05:19,550 --> 00:05:21,420 then this would do that and then if you 107 00:05:21,420 --> 00:05:24,770 print(l) then you'll see that Bob has been removed 108 00:05:24,770 --> 00:05:27,203 and you are only left with Rolf and Anne. 109 00:05:28,830 --> 00:05:31,970 Going back to adding, you can add things to a set. 110 00:05:31,970 --> 00:05:35,880 So you can do s.add("Smith") then you can print your set 111 00:05:38,480 --> 00:05:39,500 and here you can see you that you get 112 00:05:39,500 --> 00:05:42,660 Anne, Bob, Smith, and Rolf. Notice that the order is 113 00:05:42,660 --> 00:05:45,930 not the same as when we created this, but all the elements 114 00:05:45,930 --> 00:05:49,860 are there. However, if you do the same thing twice, 115 00:05:49,860 --> 00:05:52,430 you'll see that Smith will only be here once. 116 00:05:52,430 --> 00:05:54,240 That's because, even though we told the set 117 00:05:54,240 --> 00:05:57,760 to add Smith twice there can be no duplicate elements 118 00:05:57,760 --> 00:06:01,043 inside a set, so this second Smith is actually ignored. 119 00:06:02,160 --> 00:06:05,850 This was a very brief primer or refresher regarding what 120 00:06:05,850 --> 00:06:08,140 lists, tuples and sets are. 121 00:06:08,140 --> 00:06:12,290 So just remember that lists are the most standard collection 122 00:06:12,290 --> 00:06:15,250 where you add and remove elements as well as modify them. 123 00:06:15,250 --> 00:06:18,370 In a tuple you have those elements and you can't modify them 124 00:06:18,370 --> 00:06:20,270 and you can't add or remove elements. 125 00:06:20,270 --> 00:06:23,480 And finally, a set, has no duplicate elements 126 00:06:23,480 --> 00:06:25,803 and it also has no order. 127 00:06:27,000 --> 00:06:28,300 That's everything for this video. 128 00:06:28,300 --> 00:06:29,400 Thank you for joining me. 129 00:06:29,400 --> 00:06:31,050 And I'll see you in the next one.