1 00:00:05,260 --> 00:00:07,480 Welcome back, everyone, to part two of our discussion of. 2 00:00:08,500 --> 00:00:11,050 Let's get started actually coding and creating a class. 3 00:00:11,590 --> 00:00:11,860 All right. 4 00:00:11,860 --> 00:00:14,050 So here I am inside visual studio code. 5 00:00:14,530 --> 00:00:19,000 Let's begin by understanding that in Python, everything is actually an object. 6 00:00:19,330 --> 00:00:20,350 How can I prove this to you? 7 00:00:20,530 --> 00:00:26,740 Well, I'm going to say that NUM is equal to 10, and I'm going to say print. 8 00:00:27,190 --> 00:00:35,830 The type of NUM wear type is a built in function within Python that reports back the type of object 9 00:00:35,830 --> 00:00:36,730 that you passed into it. 10 00:00:37,150 --> 00:00:44,860 So if I save those changes and I run this code, I get back Class A. For an integer class, less changes 11 00:00:44,860 --> 00:00:51,940 to be something like ten point three saved that change and run this and I see this as a float class 12 00:00:51,940 --> 00:00:54,790 object and maybe less changes to be a string. 13 00:00:55,360 --> 00:00:58,510 So we'll say 200, but it's around that in quotes. 14 00:00:59,230 --> 00:01:03,070 Next, I run this and I can see this is class STR for string. 15 00:01:03,640 --> 00:01:06,520 Now, clearly everything in Python is an object. 16 00:01:06,850 --> 00:01:10,810 Now the question arises How do we get to define our own objects? 17 00:01:10,960 --> 00:01:14,410 And that's where we have to use the class keyword and to come back here. 18 00:01:14,800 --> 00:01:16,120 Let's go ahead and clear this out. 19 00:01:16,570 --> 00:01:19,820 And let's begin by creating probably the simplest class possible. 20 00:01:19,840 --> 00:01:25,780 I call the class keyword and then by convention classes are capitalized and follow camel casing. 21 00:01:26,350 --> 00:01:30,010 So we're going to call this our sample class open and close parentheses. 22 00:01:30,640 --> 00:01:33,370 And keep in mind that you don't technically need parentheses here. 23 00:01:33,550 --> 00:01:37,570 You could also just say Colon, but I like open and close parentheses. 24 00:01:38,080 --> 00:01:39,060 And I'll show you why. 25 00:01:39,070 --> 00:01:40,750 Later on, we learn about inheritance. 26 00:01:40,750 --> 00:01:45,130 But again, keep in mind, technically speaking, you don't need these parentheses here, which is why 27 00:01:45,160 --> 00:01:47,590 sometimes you don't actually see this and documentation. 28 00:01:48,070 --> 00:01:50,710 But moving along, what I'll do is I'll simply put pass. 29 00:01:52,030 --> 00:01:54,820 So this is just a keyword in Python says Pass. 30 00:01:54,820 --> 00:01:55,690 Don't do anything. 31 00:01:55,780 --> 00:02:00,550 Essentially, this class does nothing except define itself as a sample class. 32 00:02:01,030 --> 00:02:04,120 Let's make what's known as an instance of a class. 33 00:02:04,390 --> 00:02:09,100 So I'm going to say now NUM is equal to an instance of sample. 34 00:02:09,220 --> 00:02:12,130 So I say sample open, close parentheses. 35 00:02:12,580 --> 00:02:15,580 And now let's print out the type of NUM. 36 00:02:15,970 --> 00:02:18,400 Notice how similar this is what we just said previously. 37 00:02:18,610 --> 00:02:23,620 Except this time, instead of calling this a float or integer or string, we're actually defining it 38 00:02:23,620 --> 00:02:25,510 as our own user defined class. 39 00:02:25,960 --> 00:02:28,570 Also, be very careful to note my indentation here. 40 00:02:28,990 --> 00:02:34,270 Classes are kind of like functions in the sense that everything indented is part of the class. 41 00:02:34,690 --> 00:02:39,610 Here I have this in line with the class call, and if you're confused, you can always use the collapse 42 00:02:39,610 --> 00:02:43,030 method here to see what code is actually inside the class. 43 00:02:43,570 --> 00:02:50,110 But now I saved this and I run this and I can see it says, Hey, this is class main. 44 00:02:50,320 --> 00:02:56,170 The sample main is actually a reference to the fact that it's running within the same Python file that 45 00:02:56,170 --> 00:02:57,010 it was defined then. 46 00:02:57,400 --> 00:03:01,210 And then sample is just telling you this is an instance of the sample class. 47 00:03:01,570 --> 00:03:01,930 All right. 48 00:03:02,320 --> 00:03:07,900 So now we understand this idea that in Python, everything is an object, and I can use this class keyword 49 00:03:08,170 --> 00:03:11,260 to actually define my own objects. 50 00:03:11,560 --> 00:03:12,670 So what's next? 51 00:03:13,060 --> 00:03:16,120 Well, we need to do is sometimes to find attributes. 52 00:03:16,510 --> 00:03:19,240 So let me show you how to define attributes within a class. 53 00:03:19,720 --> 00:03:23,080 What I'm going to do is here, inside class sample, I'm going to say. 54 00:03:24,430 --> 00:03:29,860 And instantiation method, which is a method that gets run every time you create a new instance of an 55 00:03:29,860 --> 00:03:38,710 object and it's thief underscore underscore I and I t underscore, underscore and keep in mind that 56 00:03:38,710 --> 00:03:41,170 there's two sets of underscores on each side here. 57 00:03:41,380 --> 00:03:46,390 Really common beginner mistake is that they only put one underscore and here what I'm going to do is 58 00:03:46,390 --> 00:03:49,240 I'm going to pass in the self keyword. 59 00:03:49,840 --> 00:03:52,720 The self keyword is this special keyword. 60 00:03:52,900 --> 00:03:56,620 Technically speaking, it doesn't need to be self, but by convention, we always use self. 61 00:03:56,980 --> 00:04:02,230 And this basically allows Python to understand that this particular method that we're creating and this 62 00:04:02,230 --> 00:04:04,990 is a special one called in it for instantiation. 63 00:04:05,350 --> 00:04:11,800 What's going to happen is when we actually create a instance of sample class, the self keyword is going 64 00:04:11,800 --> 00:04:17,690 to allow me to actually refer to attributes of the class from any other method in that class. 65 00:04:17,740 --> 00:04:21,820 So we're going to say self here and then I'm going to pass in one more parameter. 66 00:04:22,270 --> 00:04:25,840 And let's go ahead and have this say something like name. 67 00:04:26,650 --> 00:04:31,960 So now I can actually pass in a name upon creating an instance of sample class. 68 00:04:32,620 --> 00:04:36,790 And then here we're going to say self-taught name is equal to name. 69 00:04:37,390 --> 00:04:44,560 What I want to make clear here is if I'm attaching self-taught name to this particular variable, what 70 00:04:44,560 --> 00:04:51,010 this does is it allows self but name to later on be used within any method that we end up creating within 71 00:04:51,010 --> 00:04:54,700 the class name on this side without a self attached. 72 00:04:54,970 --> 00:05:00,310 Basically, it refers to the fact that the user, upon creating a sample class, will have to provide 73 00:05:00,310 --> 00:05:00,820 a name. 74 00:05:01,630 --> 00:05:03,400 So let me show you what I mean by that. 75 00:05:03,430 --> 00:05:07,930 I'm actually going to start calling this X just so we don't get confused with any numbers we pass in. 76 00:05:08,530 --> 00:05:13,030 And if I just run this, I should expect to see an error. 77 00:05:13,390 --> 00:05:14,830 So again, I have my class. 78 00:05:14,830 --> 00:05:21,310 I created this instantiation method in it call and it says that you have to pass in some name parameter 79 00:05:21,310 --> 00:05:23,830 and then it gets assigned to self that name attribute. 80 00:05:24,310 --> 00:05:31,450 If you just run it like this, we should get an error and it says, Hey, type error in it is missing 81 00:05:31,450 --> 00:05:33,790 one required positional argument called name. 82 00:05:34,240 --> 00:05:40,060 So now you have to actually say a name here, and we have been super clear or explicit on what this 83 00:05:40,060 --> 00:05:40,960 name actually is. 84 00:05:41,230 --> 00:05:43,150 But let's just assume that they kind of want a string. 85 00:05:44,110 --> 00:05:44,920 So I'll say that. 86 00:05:45,700 --> 00:05:51,610 And now when I run this, I can see that it's still a class main that sample, but now it has this attribute. 87 00:05:52,090 --> 00:05:57,100 And how can I actually access this attribute once this instance of the class is created? 88 00:05:57,640 --> 00:06:04,120 Well, I could say print type X, but now I can also do the following I can say print x dot. 89 00:06:05,220 --> 00:06:06,150 And then the name. 90 00:06:07,510 --> 00:06:08,110 Say that. 91 00:06:09,470 --> 00:06:11,600 Run this and now I get to see the result. 92 00:06:11,660 --> 00:06:18,260 Jose, so now we understand that if I have an attribute as part of a class call, I use Dot and then 93 00:06:18,260 --> 00:06:23,840 the attribute name and notice the similarity here we say in between saying the actual variable name, 94 00:06:24,110 --> 00:06:26,740 variable name, dot name and then self that name. 95 00:06:26,750 --> 00:06:32,330 So this syntax is reflective of what you're going to do after you instantiate that instance of the class. 96 00:06:32,720 --> 00:06:34,400 In fact, let's start changing this. 97 00:06:34,700 --> 00:06:40,770 So maybe we're trying to create a student class, so we're trying to organize a school. 98 00:06:40,820 --> 00:06:47,720 And so I create this student class and a student could have a name, and maybe a student also has a 99 00:06:47,720 --> 00:06:48,290 GPA. 100 00:06:49,070 --> 00:06:54,740 And then I want to make sure that when they pass on that, I'm actually storing it to be part of an 101 00:06:54,740 --> 00:06:55,730 attribute of the student. 102 00:06:55,730 --> 00:07:01,250 So I can say salta GPA is equal to the GPA that's passed into the user. 103 00:07:01,850 --> 00:07:04,700 So now I can actually then create instances of these objects. 104 00:07:04,700 --> 00:07:11,030 For example, I'm going to create student one as equal to Jose and will be generous myself to give myself 105 00:07:11,030 --> 00:07:14,010 a 4.0 GPA, whether or not that was actually true. 106 00:07:14,030 --> 00:07:19,580 We'll leave it up to history to decide, and we're going to say Student two is equal to and I remember 107 00:07:19,580 --> 00:07:20,840 sample's no longer the fine. 108 00:07:21,680 --> 00:07:23,300 So I have to actually call this students. 109 00:07:23,660 --> 00:07:27,200 Help me expand our space here a little bit so you can see everything I'm doing. 110 00:07:27,710 --> 00:07:33,770 So we have our student class now takes a name and GPA as attributes that are defined upon creating a 111 00:07:33,770 --> 00:07:34,250 new student. 112 00:07:34,700 --> 00:07:38,630 So Student one is named Jose GPA for Let's Create Another Student. 113 00:07:40,600 --> 00:07:42,910 The name will be say me, me. 114 00:07:44,510 --> 00:07:47,230 And this is going to be, let's say, three point five. 115 00:07:47,970 --> 00:07:52,400 OK, so if you just create those students, nothing actually really happens here. 116 00:07:52,760 --> 00:07:55,970 So if you're own Python, example that pi expanding this a little bit. 117 00:07:57,000 --> 00:08:00,390 You can see we don't actually get any sort of output because I haven't printed anything. 118 00:08:00,750 --> 00:08:06,270 So what I can do is let's go ahead and say print student one dot GPA. 119 00:08:07,950 --> 00:08:08,880 Save that change. 120 00:08:09,420 --> 00:08:15,750 Run this now I can see 4.0, and later on we'll actually discuss what actually happens if you want something 121 00:08:15,750 --> 00:08:16,590 more displayed. 122 00:08:16,830 --> 00:08:23,280 Because if I just say print stu one, I don't actually see name or it just says, Hey, this is a student 123 00:08:23,280 --> 00:08:25,230 object at this point in memory. 124 00:08:25,260 --> 00:08:26,400 This is not super useful. 125 00:08:26,670 --> 00:08:31,950 So later on in the series of lectures, we will discuss how to create customization for what is printed 126 00:08:31,950 --> 00:08:32,150 out. 127 00:08:32,159 --> 00:08:32,970 But just keep that in mind. 128 00:08:32,970 --> 00:08:37,679 If you actually print out an instance of an object, then you're going to see, Hey, this is a student 129 00:08:37,679 --> 00:08:39,990 object at this point in memory at your computer. 130 00:08:41,309 --> 00:08:48,040 So one thing to notice here is, unlike method calls, attributes are not actually called with parentheses. 131 00:08:48,060 --> 00:08:51,390 So I just said, Stu, that name, I did not say name. 132 00:08:51,600 --> 00:08:52,800 Open close parentheses. 133 00:08:53,190 --> 00:08:58,140 Open close princes later on will be used when we actually create new methods for that class. 134 00:08:58,500 --> 00:09:05,310 But right now, we can think of attributes as descriptors of an instance of the class, like a name 135 00:09:05,460 --> 00:09:08,550 and a describe an instance of a student. 136 00:09:09,030 --> 00:09:15,060 Now there may be something called a class object attribute, which is going to be an attribute that 137 00:09:15,060 --> 00:09:20,610 should be the same regardless of the actual instance of the class. 138 00:09:20,880 --> 00:09:26,970 So, for example, what would be true for any student at the school that maybe their name will be different, 139 00:09:26,970 --> 00:09:28,640 but their GPA will also be different. 140 00:09:28,650 --> 00:09:31,830 But I want something that's going to be true for any instance of a student. 141 00:09:32,220 --> 00:09:33,870 So what could I do for something like that? 142 00:09:34,140 --> 00:09:37,800 Maybe I could just say that all students are going to be human students. 143 00:09:37,920 --> 00:09:39,750 So this is not a school for dogs. 144 00:09:40,200 --> 00:09:46,350 So maybe I say something like species is equal to and then say human. 145 00:09:46,920 --> 00:09:48,510 Or maybe they're all on planet Earth. 146 00:09:48,690 --> 00:09:54,060 So I say, OK, for all these students, their planet is going to be Earth. 147 00:09:55,140 --> 00:09:56,880 So what's kind of special to note here? 148 00:09:57,330 --> 00:10:02,340 You should know that this is known as a class object attribute. 149 00:10:02,850 --> 00:10:11,640 So this is a class object attribute and this is different than name and GPA here, which are just attributes. 150 00:10:11,850 --> 00:10:12,750 So what's the difference? 151 00:10:13,080 --> 00:10:14,760 The difference is for one. 152 00:10:14,790 --> 00:10:17,790 This actually doesn't go inside the init call. 153 00:10:18,120 --> 00:10:22,830 If you want an attribute that is going to be the same for every instance of an object you create. 154 00:10:23,130 --> 00:10:25,740 You actually put it outside the init call. 155 00:10:26,190 --> 00:10:30,760 The other thing you should know is it doesn't actually need self-talk. 156 00:10:31,530 --> 00:10:38,310 Why does it not need self, but, well, notice that this is going outside of any of these method calls 157 00:10:38,310 --> 00:10:39,000 that we're creating. 158 00:10:39,360 --> 00:10:45,270 So hence, it's kind of obvious to Python that, yes, planet is associated with an instance of student. 159 00:10:45,630 --> 00:10:48,210 It's not hidden within some sort of method. 160 00:10:48,570 --> 00:10:54,960 And the reason self is here inside this method is to make sure you have the capability to connect these 161 00:10:54,960 --> 00:11:01,230 user defined attributes to an attribute that you can later on use with an other method of calls. 162 00:11:01,770 --> 00:11:08,730 So this is a class object attribute and not what happens when I save this code and I run this again. 163 00:11:09,630 --> 00:11:10,950 I don't get any sort of error. 164 00:11:10,980 --> 00:11:16,710 Remember student one, their name is Jose, but what I can also do is say student one now and ask for 165 00:11:16,740 --> 00:11:18,750 what planet are they from? 166 00:11:20,090 --> 00:11:22,190 Run this, and now I can see it's Earth. 167 00:11:22,610 --> 00:11:26,720 Now here for student one, I didn't have to actually declare planet. 168 00:11:26,750 --> 00:11:32,420 In fact, we should expect that we never have to declare planet because the whole point of a class object 169 00:11:32,420 --> 00:11:36,860 attribute is that it's going to be the same for any instance of a students. 170 00:11:37,040 --> 00:11:41,450 And again, you can always use the collapse mechanism here to give yourself a little more space to view 171 00:11:41,720 --> 00:11:44,900 what the class has as far as attributes and methods. 172 00:11:45,410 --> 00:11:47,690 OK, so that's pretty much it. 173 00:11:47,690 --> 00:11:52,610 For this lecture, we created our first class, and along with that, we also created attributes. 174 00:11:52,940 --> 00:11:58,700 What I'm going to do is just from scratch create another class of something kind of related to students 175 00:11:58,940 --> 00:12:02,480 just to get us a little familiar with the idea of creating a class. 176 00:12:02,930 --> 00:12:09,950 Let's imagine I'm creating a secret agent class, so I'm running the CIA or some sort of secret intelligence 177 00:12:09,950 --> 00:12:10,610 agency. 178 00:12:11,030 --> 00:12:12,670 And I want to create an agent class. 179 00:12:12,670 --> 00:12:14,270 So I'm going to say class agent. 180 00:12:16,260 --> 00:12:24,780 And maybe since I'm running this at our national organization, I know that the birth or place of origin 181 00:12:24,780 --> 00:12:28,590 for all these agents is going to be United States or something like that. 182 00:12:29,100 --> 00:12:32,220 So we're going to see Origin is USA. 183 00:12:32,970 --> 00:12:36,150 So origin as USA, that means all these agents. 184 00:12:36,390 --> 00:12:40,120 I'm going to say their origin is USA, regardless of what's actually passed it. 185 00:12:40,770 --> 00:12:46,950 Then when I want to actually create an instance of an agent class automatically, the in its method 186 00:12:46,950 --> 00:12:47,790 is going to be called. 187 00:12:48,210 --> 00:12:52,080 So in that method is called upon creating an instance of agent. 188 00:12:52,680 --> 00:12:55,680 So we pass in self so we can begin to assign attributes. 189 00:12:56,280 --> 00:12:57,630 And then what else can we do here? 190 00:12:57,660 --> 00:13:01,110 Well, I can say something like maybe the agents are going to have a name. 191 00:13:01,530 --> 00:13:06,270 Maybe they have a height, and maybe they also have a weight or something like that. 192 00:13:06,690 --> 00:13:07,050 Well. 193 00:13:08,170 --> 00:13:12,910 What I do, then, is in order to accept these are these parameter calls and assign them as attributes 194 00:13:12,910 --> 00:13:17,350 as I buy conventions say the same parameter name just with herself in front of it. 195 00:13:17,590 --> 00:13:21,430 So if that name is name and then we're going to say soft that height. 196 00:13:22,490 --> 00:13:23,450 Is height. 197 00:13:24,450 --> 00:13:25,830 And then self thought, wait. 198 00:13:27,770 --> 00:13:28,820 Is wait here. 199 00:13:29,690 --> 00:13:32,480 OK, so here we have again, a very simple class. 200 00:13:33,140 --> 00:13:36,260 Every instance of an agent is going to be Origin USA. 201 00:13:36,770 --> 00:13:40,700 And then when you create an agent, you have to define their name, their height and their weight. 202 00:13:41,060 --> 00:13:43,130 So we also think of this maybe as like a patient or something. 203 00:13:43,370 --> 00:13:49,700 If I wanted to change the class, so now I'm going to create an instance of an agent so I can say X, 204 00:13:49,700 --> 00:13:52,420 for instance, is equal to an instance of an agent. 205 00:13:52,460 --> 00:13:55,370 I remember I need to define their name, their height and their weight. 206 00:13:55,460 --> 00:14:02,390 So I could say something like Kosi weight or height two six and then weights is 170 or something like 207 00:14:02,390 --> 00:14:02,630 that. 208 00:14:03,170 --> 00:14:05,120 We're not worried too much about the metrics right now. 209 00:14:05,270 --> 00:14:06,830 And then I can say prints. 210 00:14:07,940 --> 00:14:09,680 X name, for instance. 211 00:14:10,960 --> 00:14:14,090 Save that, and when you run this code, you should see now, Josie. 212 00:14:14,470 --> 00:14:19,150 So he created an instance of an agent that I can now actually use. 213 00:14:19,840 --> 00:14:23,620 Now I can also update the actual attributes. 214 00:14:23,860 --> 00:14:26,670 So let's say the agent lost some weight. 215 00:14:26,680 --> 00:14:36,790 I could say x dot weight is equal to 160 and then print out x that weight. 216 00:14:37,210 --> 00:14:42,760 So this is one way of actually grabbing an attribute and then updating it just to prove to you that 217 00:14:42,760 --> 00:14:43,600 the update works. 218 00:14:44,050 --> 00:14:45,880 Before I update, I will print. 219 00:14:46,900 --> 00:14:47,720 It's that way. 220 00:14:47,740 --> 00:14:53,320 So notice what I'm doing, I'm initially defining Jose having weight 170, I print out that weight. 221 00:14:53,590 --> 00:14:56,500 The uptake happens and then I print out the new updated weight. 222 00:14:56,770 --> 00:15:01,000 So I start see 170 and then 160 to show that the update worked. 223 00:15:02,180 --> 00:15:07,250 And there it is, 170 upon creation, and then later on, I updated it using one 60. 224 00:15:07,640 --> 00:15:14,630 So clearly there's this idea of I'm able to grab attributes, report them, and I can also update attributes. 225 00:15:15,050 --> 00:15:20,390 Keep in mind, we shouldn't really keep keeping the effect of updating class object attributes. 226 00:15:20,390 --> 00:15:21,890 That's not really what they're there for. 227 00:15:22,640 --> 00:15:25,340 So that is the basics of creating a class. 228 00:15:25,670 --> 00:15:29,030 The instantiation method that can then allow us to define attributes. 229 00:15:29,420 --> 00:15:33,560 Coming up next, we're going to learn about methods which are essentially functions defined inside the 230 00:15:33,560 --> 00:15:34,550 body of a class. 231 00:15:34,940 --> 00:15:39,260 And then it's going to make a lot more sense why we can use things like self that name instead of just 232 00:15:39,260 --> 00:15:39,620 name. 233 00:15:40,070 --> 00:15:41,540 OK, I'll see you at the next lecture.