1 00:00:04,120 --> 00:00:09,820 So let's go back now, to our Mutable Sequence Types Python documentation page, 2 00:00:09,820 --> 00:00:14,690 and looking at that, it might look quite confusing. The first five operations are 3 00:00:14,690 --> 00:00:19,759 using indexing and slicing, to change items in the sequence. Make sure that 4 00:00:19,759 --> 00:00:24,050 you're happy using indexes and slices. Review the videos in section 3, if 5 00:00:24,050 --> 00:00:29,000 necessary, because we'll be using slices later in this section. I'm not going to 6 00:00:29,000 --> 00:00:32,540 discuss them just yet, because changing slices will be easier 7 00:00:32,540 --> 00:00:36,890 to understand, once we've seen lists in more detail. So I'm going to start by 8 00:00:36,890 --> 00:00:43,200 discussing the append method, which is that sixth line, here in that table. 9 00:00:43,200 --> 00:00:48,520 Now I used the term method there. A method is the same as a function, except that it's 10 00:00:48,520 --> 00:00:54,360 bound to an object. That means we need an object, in order to call the method. 11 00:00:54,360 --> 00:00:59,320 We've used a few functions in the last video: we used min and max, and the len function. 12 00:00:59,320 --> 00:01:04,040 When you call a function, you just type its name, and provide any arguments in 13 00:01:04,040 --> 00:01:07,729 parentheses. For example, len, and even in parentheses, 14 00:01:07,729 --> 00:01:13,540 gives us the number of items in the list called even. When we call a method, 15 00:01:13,540 --> 00:01:17,960 we tell it which object it's called on. In other words, which object it should be 16 00:01:17,960 --> 00:01:22,610 using when it performs its function. For example, the entry we're looking at, in 17 00:01:22,610 --> 00:01:28,640 the table, is s.append and x in parentheses. So that means that we'll be 18 00:01:28,640 --> 00:01:35,210 appending x to a list called s. We pass x as an argument, so that the method knows 19 00:01:35,210 --> 00:01:39,799 what to append, but we don't have to use an argument to tell it which list to 20 00:01:39,799 --> 00:01:46,070 append to, because that comes at the start, before the dot. Dot notation's used 21 00:01:46,070 --> 00:01:50,600 a lot in Object Oriented Programming, and we'll learn more about in the OOP 22 00:01:50,600 --> 00:01:54,710 section of this course. Before we learn how to write our own methods, we'll be 23 00:01:54,710 --> 00:01:59,420 using a lot of methods that Python's built-in objects have. The syntax is 24 00:01:59,420 --> 00:02:04,280 simple. You start with the object you're using, then a dot, then the name of the 25 00:02:04,280 --> 00:02:10,960 method. If the method needs arguments, you put them in parentheses after the method name. 26 00:02:10,960 --> 00:02:15,620 So we start with the name of an object. The documentation uses s because 27 00:02:15,620 --> 00:02:20,599 it's talking about sequence types. After the dot, we have the name of the 28 00:02:20,599 --> 00:02:26,060 method that we want to call, in this case, append. If the method needs any arguments, 29 00:02:26,060 --> 00:02:30,500 they appear in parentheses after the method name. The parentheses are still 30 00:02:30,500 --> 00:02:34,370 needed, even if there are no arguments. That's the same as when you call a 31 00:02:34,370 --> 00:02:39,560 function. Alright, so back to the code now. The append method can be used to add a 32 00:02:39,560 --> 00:02:44,750 new item to a list. Now we used append in the mutable.py program that we've 33 00:02:44,750 --> 00:02:49,820 written previously, so let's go and open that up - specifically down here, on line 21. 34 00:02:49,820 --> 00:02:54,920 That appended cream, in this case, to our list. So run the program again, just so we 35 00:02:54,920 --> 00:03:01,069 can see what's happening. When the list is printed on line 18, it contains seven 36 00:03:01,069 --> 00:03:05,900 items. Line 20 prints the message Adding cream, to make it easier to see what's 37 00:03:05,900 --> 00:03:11,090 happening in the output, and line 21 uses the append method to add cream to the 38 00:03:11,090 --> 00:03:16,790 end of the list. So moving on, on lines 22 and 23, when we print the list it now 39 00:03:16,790 --> 00:03:20,340 contains cream, and you can see that in the output down the bottom of the screen. 40 00:03:20,340 --> 00:03:24,100 Alright, so we've seen what methods are. They're functions that belong to an 41 00:03:24,109 --> 00:03:28,579 object. In this case, the append method belongs to anything that's a mutable 42 00:03:28,579 --> 00:03:33,350 sequence type. We've also talked about dot notation, which is used when you want 43 00:03:33,350 --> 00:03:37,579 to call an object's methods. In the next video, we'll write a simple program to 44 00:03:37,579 --> 00:03:43,000 demonstrate using append on a list. See you in the next video.