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These are the user uploaded subtitles that are being translated: 1 1 00:00:05,560 --> 00:00:09,580 so there's several different programming paradigms and up until now in this 2 2 00:00:09,580 --> 00:00:13,070 course we've been mainly using the imperative style of programming 3 3 00:00:13,070 --> 00:00:17,740 imperative programming involves providing a series of instructions for 4 4 00:00:17,740 --> 00:00:22,140 the computer to follow in a defined order now object oriented programming 5 5 00:00:22,140 --> 00:00:28,060 aims to combine data and the processes that act on that data into objects which is 6 6 00:00:28,060 --> 00:00:30,090 called encapsulation 7 7 00:00:30,090 --> 00:00:34,020 before I continue it's important to realize that the different paradigms are 8 8 00:00:34,020 --> 00:00:38,180 not necessarily exclusive and object-oriented programming makes use of 9 9 00:00:38,180 --> 00:00:42,050 imperative programming within the methods that objects used to manipulate 10 10 00:00:42,050 --> 00:00:48,070 the data also as we will see shortly our imperative programming in Python has 11 11 00:00:48,070 --> 00:00:53,160 actually made extensive use of objects we just didn't know that so the approach that 12 12 00:00:53,160 --> 00:00:58,190 we've been using so far in the course is very similar to a recipe for cooking a 13 13 00:00:58,190 --> 00:01:02,340 meal so the recipe starts with the ingredients and utensils it will be need 14 14 00:01:02,340 --> 00:01:07,100 which corresponds to a programs data and then continues with the description of 15 15 00:01:07,100 --> 00:01:11,520 the steps that must be performed on that data to produce in this case for the 16 16 00:01:11,520 --> 00:01:12,260 recipe 17 17 00:01:12,260 --> 00:01:17,120 finished meal an object oriented approach relies on the objects such as 18 18 00:01:17,120 --> 00:01:22,260 the eggs milk spoon etc knowing how to perform certain operations so 19 19 00:01:22,260 --> 00:01:24,640 the program just tells them to do so 20 20 00:01:24,640 --> 00:01:29,630 concept of an egg that knows how to fry itself is a little bizarre but that 21 21 00:01:29,630 --> 00:01:33,190 really shows that the imperatives approach to cooking a meal is more 22 22 00:01:33,190 --> 00:01:36,190 appropriate than an object-oriented approach 23 23 00:01:36,910 --> 00:01:40,900 now a good example of the encapsulation of data and function might be self lighting 24 24 00:01:40,900 --> 00:01:44,310 cigarettes well actually its a bad example and I certainly wouldn't 25 25 00:01:44,310 --> 00:01:48,840 want to suggest that smoking is good but it does demonstrate the concept quite well 26 26 00:01:48,840 --> 00:01:53,720 so without object oriented programming the steps to smoking a cigarette might 27 27 00:01:53,720 --> 00:01:58,540 be place cigarette in mouth that's number one number two light match number three 28 28 00:01:58,540 --> 00:02:03,650 hold match to cigarette and number four inhale now encapsulating the functions 29 29 00:02:03,650 --> 00:02:08,460 that can be performed on the cigarette into the cigarette reduces the code to 30 30 00:02:08,460 --> 00:02:14,230 place cigarette in mouth and inhale so the cigarette knows how to light itself so 31 31 00:02:14,230 --> 00:02:17,190 that's not something that the smoker needs to be concerned with 32 32 00:02:17,190 --> 00:02:21,960 the details of how it lights itself are built into it when it's manufactured or 33 33 00:02:21,960 --> 00:02:25,610 in the case of programming it's programmed into it when it's defined 34 34 00:02:25,610 --> 00:02:30,250 and the actual implementation is of no interest to anything that uses the 35 35 00:02:30,250 --> 00:02:34,470 object now I've exercise a little license they're self lighting cigarettes were 36 36 00:02:34,470 --> 00:02:38,990 produced for short time the 1960's coincidentally around the same time that 37 37 00:02:38,990 --> 00:02:43,280 object oriented programming was conceived and had a igniter 38 38 00:02:43,280 --> 00:02:48,310 built into them that had to be struck like a match the advanced type that I described only 39 39 00:02:48,310 --> 00:02:53,380 existed in science fiction stories now modern electronic cigarettes take this 40 40 00:02:53,380 --> 00:02:56,790 concept a little bit further but it's only the details of the implementation 41 41 00:02:56,790 --> 00:03:01,560 that have changed so the method use remains pretty much the same as the 42 42 00:03:01,560 --> 00:03:06,690 science-fiction variety now that's important concept of object oriented 43 43 00:03:06,690 --> 00:03:11,030 programming as we will see replacing one object with another one that performs 44 44 00:03:11,030 --> 00:03:15,330 the same task without having to concern ourselves with the details of how it 45 45 00:03:15,330 --> 00:03:20,850 performs the task is central to object oriented programming so another and 46 46 00:03:20,850 --> 00:03:25,170 hopefully much more healthier example might be an electric kettle now the 47 47 00:03:25,170 --> 00:03:29,980 imperative approach to boiling water for hot drink might be step 1 fill kettle with 48 48 00:03:29,980 --> 00:03:30,570 water 49 49 00:03:30,570 --> 00:03:37,360 step 2 light stove step 3 place kettle on stove step 4 for monitor kettle until 50 50 00:03:37,360 --> 00:03:41,970 water boils step 5 make the drink now it would then have to be a function that 51 51 00:03:41,970 --> 00:03:45,610 deals with lighting the stove which might involve further functions to collect 52 52 00:03:45,610 --> 00:03:50,780 water or coal or was switched on the gas a function to light the match and so on but 53 53 00:03:50,780 --> 00:03:55,450 in object orientated terms a kettle would have a boil method that is triggered by 54 54 00:03:55,450 --> 00:03:59,890 operating a switch so the object oriented program comes down to step 55 55 00:03:59,890 --> 00:04:01,320 one fill kettle with water 56 56 00:04:01,320 --> 00:04:07,630 step 2 switch kettle on step 3 when kettle switches off make drink so the 57 57 00:04:07,630 --> 00:04:11,030 imperative approach will also have to identify the type of stove being used as 58 58 00:04:11,030 --> 00:04:15,290 its futile and probably a bit dangerous to hold a match to electric cooker 59 59 00:04:15,290 --> 00:04:20,040 now these examples may make it look like we've got something for nothing because 60 60 00:04:20,040 --> 00:04:23,910 performing the tasks using an object oriented approach involves fewer steps 61 61 00:04:23,910 --> 00:04:28,970 but there's no magic involved here now the steps are still had to be programmed 62 62 00:04:28,970 --> 00:04:33,280 but their built into the objects so that anything that using the object doesn't have to be 63 63 00:04:33,280 --> 00:04:37,970 concerned about them so the object orientated kettle has been built to contain an 64 64 00:04:37,970 --> 00:04:41,950 element or whatever method it employs could be a ceramic disc or even a small 65 65 00:04:41,950 --> 00:04:46,600 nuclear reactor and the operation of the heating mechanism has been wired up to 66 66 00:04:46,600 --> 00:04:51,180 the switch where the kettle was made so a lot of work has gone into the production on 67 67 00:04:51,180 --> 00:04:55,370 the kettle in other words far more so that the work that goes into making a kettle 68 68 00:04:55,370 --> 00:04:59,370 for use on the stove but subsequent use of the kettle is there much easier 69 69 00:04:59,370 --> 00:05:04,010 because it knows how to perform its function itself so one thing that may 70 70 00:05:04,010 --> 00:05:09,660 not be obvious and I haven't yet mentioned is that everything in Python is an object so Python 71 71 00:05:09,660 --> 00:05:15,380 is unusual in this respect because even though Python uses objects extensively you 72 72 00:05:15,380 --> 00:05:19,480 don't actually have to be aware of that to use so Python can be used for 73 73 00:05:19,480 --> 00:05:24,010 object-oriented programming but can also be used to write purely imperative 74 74 00:05:24,010 --> 00:05:29,350 programming code so in fact the Wikipedia entry for Python which I'm going to just load 75 75 00:05:29,350 --> 00:05:37,320 up the screen now you can see the link in the top left hand corner you can see 76 76 00:05:37,320 --> 00:05:42,590 just down here it says that Python supports multiple programming paradigms 77 77 00:05:42,590 --> 00:05:46,650 including object oriented imperative and functional programming or procedural 78 78 00:05:46,650 --> 00:05:52,330 styles so in Java which is considered a class-based object-oriented language 79 79 00:05:52,330 --> 00:05:54,760 there are primitive types such as an 80 80 00:05:54,760 --> 00:05:59,070 int and a double so if you've come to Python from Java the following code which I'm 81 81 00:05:59,070 --> 00:06:05,040 about to show might seem very odd at first so lets just go back to IntelliJ and I've created a 82 82 00:06:05,040 --> 00:06:10,350 new project here and a new Python file so if you come back come from Java type in 83 83 00:06:10,350 --> 00:06:20,720 code like this.... 84 84 00:06:20,720 --> 00:06:30,150 ....so if we just run this see that it does 85 85 00:06:30,150 --> 00:06:38,070 work and we get the same result each time so line 3...and 86 86 00:06:38,070 --> 00:06:41,190 that's pretty normal for a programming language like Java 87 87 00:06:41,190 --> 00:06:47,640 but the code on line 4 would probably be a bit bizarre and that's because the a even though 88 88 00:06:47,640 --> 00:06:52,060 it's been defined as you can see on line 12 as a number you could see that a has 89 89 00:06:52,060 --> 00:06:56,180 got an add method even though its an integer so if I command click add 90 90 00:06:57,210 --> 00:07:02,540 and that is control click on a PC or Linux you can see that there's a method this is the 91 91 00:07:02,540 --> 00:07:07,600 built-ins definition of the add method and interestingly enough if I go back to oop 92 92 00:07:07,600 --> 00:07:14,330 our file and click on the plus note that it has gone to the same method in the built ins 93 93 00:07:14,330 --> 00:07:19,200 so what you can see by that is that whether you use this __add__ 94 94 00:07:19,200 --> 00:07:23,760 or use a plus it's calling the same code that is built-in 95 95 00:07:23,760 --> 00:07:29,390 builtins.py file and in this case add two numbers together and smart enough to 96 96 00:07:29,390 --> 00:07:33,440 figure out the parameters you can see there that the second argument in the 97 97 00:07:33,440 --> 00:07:38,740 case of line 3 is then added and line 4 the parameters b is added to the value 98 98 00:07:38,740 --> 00:07:43,570 of a now if this is your first programming language and either you see 99 99 00:07:43,570 --> 00:07:47,650 nothing at all strange about this or it will make very little sense but don't worry 100 100 00:07:47,650 --> 00:07:52,080 I'm gonna explain what it all means but I wanted to warn you that you know if 101 101 00:07:52,080 --> 00:07:56,690 you've come from other programming languages such as Java or C++ you 102 102 00:07:56,690 --> 00:08:00,450 probably gonna see some aspects of Python that seem surprising to you at 103 103 00:08:00,450 --> 00:08:04,210 least initially now when I said that everything in Python is an object I meant 104 104 00:08:04,210 --> 00:08:09,340 everything even types are implemented as classes now I will come 105 105 00:08:09,340 --> 00:08:13,100 back to that but for now I'm gonna focus on making sense of what I've just done 106 106 00:08:13,100 --> 00:08:19,250 their so object-oriented programming uses classes and methods to provide object 107 107 00:08:19,250 --> 00:08:24,310 that encapsulates both data and the functions that operate on that Data now the 108 108 00:08:24,310 --> 00:08:28,030 method is just another word for function and you have seen me use those terms 109 109 00:08:28,030 --> 00:08:32,940 interchangeably in this course but being big correct here when a function is part of 110 110 00:08:32,940 --> 00:08:37,350 a class in Python we call it a method now in Python there is a slight 111 111 00:08:37,350 --> 00:08:41,320 difference between a function and a method but writing a method is the same 112 112 00:08:41,320 --> 00:08:45,660 as writing functions now what we gonna do is start with a very simple example 113 113 00:08:45,660 --> 00:08:51,060 to introduce the concept of a class and show how classes work in Python now this 114 114 00:08:51,060 --> 00:08:53,920 example be a simple implementation of the electric 115 115 00:08:53,920 --> 00:08:58,260 kettle so let's go ahead and do that's so close the run window and I'm just gonna 116 116 00:08:58,260 --> 00:09:05,380 delete this code and we start by creating a kettle class and its gonna model an 117 117 00:09:05,380 --> 00:09:06,510 electric kettle 118 118 00:09:06,510 --> 00:09:16,950 so.....and notice how its has been indented for us 119 119 00:09:16,950 --> 00:09:19,950 automatically and we're going to create a method so.... 120 120 00:09:21,130 --> 00:09:29,440 .... 121 121 00:09:29,440 --> 00:09:32,320 ....will talk about this shortly... 122 122 00:09:32,320 --> 00:09:39,490 we just type in the code for now so... 123 123 00:09:39,490 --> 00:09:42,490 .... 124 124 00:09:43,390 --> 00:09:50,070 ...so looking at this it can be helpful to think of a class as a template from 125 125 00:09:50,070 --> 00:09:55,150 which objects can be created so when we create objects of this kettle class they 126 126 00:09:55,150 --> 00:10:00,290 all have a name and a price now they won't have the same name nor the same price 127 127 00:10:00,290 --> 00:10:06,390 each instance of the class will have its own values for name and price so classes 128 128 00:10:06,390 --> 00:10:10,650 as I said is a template from which objects can be created and all the objects 129 129 00:10:10,650 --> 00:10:15,670 created from the same class will share the same characteristics now an instance 130 130 00:10:15,670 --> 00:10:21,760 is just another name for an object created from a class definition so if I now create a 131 131 00:10:21,760 --> 00:10:27,480 kettle called Kenwood then Kenwood will be an instance of the kettle class you can also 132 132 00:10:27,480 --> 00:10:32,440 say that kenwood is an object of type kettle so I'm gonna create a couple of 133 133 00:10:32,440 --> 00:10:37,050 kettle objects so we can see this in practice so let's continue typing and 134 134 00:10:37,050 --> 00:10:45,190 we will go to line 8 here and type... 135 135 00:10:45,190 --> 00:11:11,950 .... 136 136 00:11:11,950 --> 00:11:18,320 ..... 137 137 00:11:18,320 --> 00:11:22,770 .....and lets make another kettle... 138 138 00:11:22,770 --> 00:11:35,290 ...and I should really have two lines there 139 139 00:11:35,290 --> 00:11:39,700 separating the class definition to be consistent with our code so the code on 140 140 00:11:39,700 --> 00:11:45,290 line 9 creates an instance of the kettle class and we've given it the name 141 141 00:11:45,290 --> 00:11:49,750 kenwood and other instances is created on line 16 and this time it's called the 142 142 00:11:49,750 --> 00:11:55,230 Hamilton so each instance has its own values for naming and price and their access 143 143 00:11:55,230 --> 00:12:00,200 by using . annotations so we type in Kenwood.price or Hamilton.make for 144 144 00:12:00,200 --> 00:12:06,240 argument sake to access that information so a good analogy here is for plans for 145 145 00:12:06,240 --> 00:12:10,880 building a house so the plan itself just describes what the house will look like 146 146 00:12:10,880 --> 00:12:15,340 its size how many rooms it will have etc now this is similar 147 147 00:12:15,340 --> 00:12:20,060 the plan to the class which is just a template for creating objects once you 148 148 00:12:20,060 --> 00:12:23,940 have a plan you can then create it as many houses as you want based on that 149 149 00:12:23,940 --> 00:12:29,170 plan and the same is true of classes once a class has been defined like how 150 150 00:12:29,170 --> 00:12:33,630 kettle class that we define on line one we can then create as many instances of that 151 151 00:12:33,630 --> 00:12:38,340 classes as we want now just as you can't do anything with the house plan other than 152 152 00:12:38,340 --> 00:12:42,330 build houses based on it you can't really do anything with the class other 153 153 00:12:42,330 --> 00:12:47,360 than create instances of it once the instances have been created you can then call 154 154 00:12:47,360 --> 00:12:53,210 their methods and access their variables so on line 11 Kenwood.price retrieves 155 155 00:12:53,210 --> 00:12:58,260 the price from the instance called Kenwood and Hamilton.price will get the 156 156 00:12:58,260 --> 00:13:03,490 price of the Hamilton instance we can also give the price a new value as we see on line 157 157 00:13:03,490 --> 00:13:10,480 13 where we set the price to $12.75 so we've been using dot notation extensively in our 158 158 00:13:10,480 --> 00:13:12,050 programs in this course 159 159 00:13:12,050 --> 00:13:16,000 when you seen that when we've used the append method to add items to a list for example 160 160 00:13:16,000 --> 00:13:22,070 also all the TK widgets are objects that have .pack and grid methods amongst 161 161 00:13:22,070 --> 00:13:26,640 many others to allow them to be placed in the window manager so lets add another 162 162 00:13:26,640 --> 00:13:31,380 example in this program so I'm going to start typing and put on some code on line 18 163 163 00:13:31,380 --> 00:13:34,570 gonna type... 164 164 00:13:46,250 --> 00:13:59,400 ..... 165 165 00:13:59,400 --> 00:14:11,670 ....and you can see here models kenwood equals$12.75 and Hamilton equals $14.55 so it's 166 166 00:14:11,670 --> 00:14:16,080 retrieved the values out of each instance of the 2 kettle objects that 167 167 00:14:16,080 --> 00:14:22,690 we've created so the parameters in the format method are the make price data attributes of 168 168 00:14:22,690 --> 00:14:26,630 the Kenwood and Hamilton objects another bit of jargon here the 169 169 00:14:26,630 --> 00:14:30,700 attributes so we've become used to talking about variables but when a 170 170 00:14:30,700 --> 00:14:35,020 variable is bound to an instance of a class then it's referred to as a data 171 171 00:14:35,020 --> 00:14:39,740 attribute in Python now their other object-oriented programming terms for 172 172 00:14:39,740 --> 00:14:44,110 the same things you might find variable attributes also called fields in 173 173 00:14:44,110 --> 00:14:49,600 languages such as Java or data members in C++ now I'll introduced yet another term 174 174 00:14:49,600 --> 00:14:53,320 shortly probably in the next video one that's been borrowed from the small talk 175 175 00:14:53,320 --> 00:14:58,940 language but lets end this video here and in then next video we'll continue our discussion about 176 176 00:14:58,940 --> 00:15:00,460 objects see you in the next video 20795