1 00:00:05,620 --> 00:00:07,520 Now as we saw in the previous videos 2 00:00:07,520 --> 00:00:08,650 in this section, 3 00:00:08,650 --> 00:00:11,380 Python classes don't need getters and setters 4 00:00:11,380 --> 00:00:13,280 to allow you to read and change the values 5 00:00:13,280 --> 00:00:15,030 of their data attributes 6 00:00:15,030 --> 00:00:17,680 or instance variables if you're more familiar with that term 7 00:00:17,680 --> 00:00:20,040 from other programming languages. 8 00:00:20,040 --> 00:00:21,490 Python adopts the philosophy 9 00:00:21,490 --> 00:00:23,570 that we're all responsible adults 10 00:00:23,570 --> 00:00:25,420 so it doesn't have the facility 11 00:00:25,420 --> 00:00:27,800 to make class attributes private 12 00:00:27,800 --> 00:00:30,660 like many other object oriented languages do. 13 00:00:30,660 --> 00:00:31,550 Now with that said, 14 00:00:31,550 --> 00:00:34,090 getters and setters are still useful in Python, 15 00:00:34,090 --> 00:00:36,630 even if they're not essential so in this video, 16 00:00:36,630 --> 00:00:38,440 we're gonna take a look at what they are, 17 00:00:38,440 --> 00:00:41,500 how to create them, and why you might want to do so. 18 00:00:41,500 --> 00:00:42,780 Now I'm gonna start off 19 00:00:42,780 --> 00:00:45,430 by doing something quite controversial. 20 00:00:45,430 --> 00:00:49,350 I'm gonna put each of our classes in a separate file. 21 00:00:49,350 --> 00:00:53,250 Now this is the usual way of doing things in C++ or Java, 22 00:00:53,250 --> 00:00:56,570 but there's no need to have one file per class in Python. 23 00:00:56,570 --> 00:00:57,400 And in fact, 24 00:00:57,400 --> 00:00:59,780 if I was creating these classes in a working programme, 25 00:00:59,780 --> 00:01:02,970 I would actually keep them all in the same file. 26 00:01:02,970 --> 00:01:04,560 But the reason I'm gonna do that here 27 00:01:04,560 --> 00:01:06,830 is because we're gonna be flicking back and forth 28 00:01:06,830 --> 00:01:08,600 looking at the various classes 29 00:01:08,600 --> 00:01:10,450 while I describe what's going on 30 00:01:10,450 --> 00:01:12,170 and that's much easier to do 31 00:01:12,170 --> 00:01:14,680 if each class appears in its own tab in the editor 32 00:01:14,680 --> 00:01:17,400 rather than scrolling up and down through a single file. 33 00:01:17,400 --> 00:01:20,020 And it also provides an excuse to show you another way 34 00:01:20,020 --> 00:01:21,650 of importing a class. 35 00:01:21,650 --> 00:01:22,480 So I'm doing it here 36 00:01:22,480 --> 00:01:25,480 but remember that it's not necessary to do this in Python. 37 00:01:25,480 --> 00:01:28,300 You're better off keeping related classes in the same file 38 00:01:28,300 --> 00:01:31,850 so that each file is organised based on functionality. 39 00:01:31,850 --> 00:01:33,600 Okay, so we're gonna use the characters 40 00:01:33,600 --> 00:01:36,210 in a role playing type game for our examples 41 00:01:36,210 --> 00:01:38,280 so let's create a new Python project. 42 00:01:38,280 --> 00:01:40,750 We're gonna call it game. 43 00:01:40,750 --> 00:01:42,830 Python is selected there. 44 00:01:43,720 --> 00:01:44,550 Game. 45 00:01:48,840 --> 00:01:50,450 Now our first class is gonna be used 46 00:01:50,450 --> 00:01:52,820 to represent the people playing the game 47 00:01:52,820 --> 00:01:56,760 so let's create a new Python file called player.py 48 00:01:56,760 --> 00:01:58,860 so I'm just gonna come over here as normal, 49 00:01:58,860 --> 00:02:02,720 right click, new, Python file, file I should say, 50 00:02:02,720 --> 00:02:05,220 player is the name, all right. 51 00:02:07,580 --> 00:02:09,580 So each player is gonna have a name 52 00:02:09,580 --> 00:02:12,130 as well as things like the number of lives they've got left 53 00:02:12,130 --> 00:02:13,400 and their score. 54 00:02:13,400 --> 00:02:16,160 So we're gonna start with this basic player class. 55 00:02:16,160 --> 00:02:20,330 So we're gonna type class Player object colon enter enter 56 00:02:23,640 --> 00:02:27,800 and then we're gonna do def space underscore underscore init 57 00:02:28,840 --> 00:02:31,800 and you saw that I just selected that for ourself, 58 00:02:31,800 --> 00:02:34,640 but then I also need to do a semicolon and a name 59 00:02:34,640 --> 00:02:38,810 for the parameter and we're gonna do self.name equals name 60 00:02:41,230 --> 00:02:45,090 then we're gonna do self.lives is equal to three, 61 00:02:45,090 --> 00:02:49,260 self.level is equal to one and self.score equals zero. 62 00:02:52,770 --> 00:02:54,440 So the convention is that class name 63 00:02:54,440 --> 00:02:56,160 should start with a capital letter, 64 00:02:56,160 --> 00:02:58,340 although some of the built-in classes in Python 65 00:02:58,340 --> 00:03:00,180 don't follow that convention. 66 00:03:00,180 --> 00:03:03,290 Now this is a very simple class with four data attributes 67 00:03:03,290 --> 00:03:05,930 and their given values in the class constructor, 68 00:03:05,930 --> 00:03:07,440 the underscore underscore init, 69 00:03:07,440 --> 00:03:09,290 underscore underscore method. 70 00:03:09,290 --> 00:03:11,430 And again, that's the class constructor. 71 00:03:11,430 --> 00:03:13,770 Now we pass one of these values as a parameter 72 00:03:13,770 --> 00:03:15,500 so when we create each player, 73 00:03:15,500 --> 00:03:18,070 they're given a name when they're created. 74 00:03:18,070 --> 00:03:20,790 Now the other three values start off with default values, 75 00:03:20,790 --> 00:03:24,650 three for lives, one for level and a score of zero. 76 00:03:24,650 --> 00:03:26,240 All right, so we're going to put all the code 77 00:03:26,240 --> 00:03:29,390 that uses the classes in a file called main.py 78 00:03:29,390 --> 00:03:32,640 so let's go ahead and create that. 79 00:03:32,640 --> 00:03:36,810 We're gonna right click on new Python file, call it main, 80 00:03:39,870 --> 00:03:43,620 and the code is gonna be import space Player, 81 00:03:45,610 --> 00:03:49,780 tim equals player in lowercase dot player in uppercase 82 00:03:52,880 --> 00:03:53,960 and then tim, 83 00:03:55,750 --> 00:03:58,660 print tim.name and print tim.lives. 84 00:04:04,220 --> 00:04:06,560 Okay, now I've accidentally put a capital P in there 85 00:04:06,560 --> 00:04:09,540 for the import and it should've been lowercase P 86 00:04:09,540 --> 00:04:11,710 because the filename you can see in the top left hand corner 87 00:04:11,710 --> 00:04:14,450 has a lowercase P for the name 88 00:04:14,450 --> 00:04:16,640 so I'll just do a lowercase P 89 00:04:16,640 --> 00:04:19,260 and we can see it's now finding it 90 00:04:19,260 --> 00:04:21,570 and that error should disappear. 91 00:04:21,570 --> 00:04:25,540 All right, so just to confirm this, if we run this now, 92 00:04:25,540 --> 00:04:27,460 okay, we can see there, 93 00:04:28,390 --> 00:04:29,840 I'm gonna move this down to the bottom, 94 00:04:29,840 --> 00:04:34,460 the player's name is tim and he's got three lives. 95 00:04:34,460 --> 00:04:36,570 All right, now having to type player with lowercase 96 00:04:36,570 --> 00:04:38,470 dot player in uppercase 97 00:04:38,470 --> 00:04:40,370 every time we wanna refer to the player class 98 00:04:40,370 --> 00:04:41,810 is gonna be a bit annoying 99 00:04:41,810 --> 00:04:45,520 so we can change the way that we input the player module 100 00:04:45,520 --> 00:04:46,820 to avoid this. 101 00:04:46,820 --> 00:04:49,320 So up here on line one, let's actually change this 102 00:04:49,320 --> 00:04:50,280 instead of import player to be 103 00:04:50,280 --> 00:04:53,780 from player import Player with a capital P 104 00:04:58,630 --> 00:05:00,440 and then we can just change this definition here 105 00:05:00,440 --> 00:05:03,100 just to be tim equals Player tim 106 00:05:04,160 --> 00:05:07,850 and we can run this and we get the same result. 107 00:05:07,850 --> 00:05:10,980 So basically we can refer to the player class 108 00:05:10,980 --> 00:05:13,560 without having to qualify it with the module name. 109 00:05:13,560 --> 00:05:15,900 Now I did suggest previously 110 00:05:15,900 --> 00:05:18,050 that you don't use this kind of import 111 00:05:18,050 --> 00:05:20,400 and generally I wouldn't recommend it. 112 00:05:20,400 --> 00:05:21,460 But here though, 113 00:05:21,460 --> 00:05:24,450 each module is only gonna contain a single class 114 00:05:24,450 --> 00:05:26,650 so there's really not gonna be any confusion 115 00:05:26,650 --> 00:05:28,750 about where a player is coming from. 116 00:05:28,750 --> 00:05:29,580 Now as I've said, 117 00:05:29,580 --> 00:05:32,320 you probably wouldn't place each class in its own file, 118 00:05:32,320 --> 00:05:34,880 but as we are doing that to this exercise, 119 00:05:34,880 --> 00:05:38,060 we may as well make it a lot easier for ourselves. 120 00:05:38,060 --> 00:05:41,410 All right, so we've got a basic player class 121 00:05:41,410 --> 00:05:43,640 and we could take lives away from the players 122 00:05:43,640 --> 00:05:45,350 as we get into scraps and take damage 123 00:05:45,350 --> 00:05:47,740 from the monsters that they'll be fighting. 124 00:05:47,740 --> 00:05:51,120 So we can do something like here on line seven 125 00:05:51,120 --> 00:05:53,280 tim.lives minus equals one 126 00:05:55,320 --> 00:05:58,100 which is obviously going to deduct the number of lives, 127 00:05:58,100 --> 00:05:59,810 one from the number of lives, 128 00:05:59,810 --> 00:06:04,240 and print out tim.lives and if you run this, 129 00:06:04,240 --> 00:06:06,280 we get this at the bottom of the screen 130 00:06:06,280 --> 00:06:10,310 showing the lives has been decremented and it's now two. 131 00:06:10,310 --> 00:06:12,000 So this is making fine 132 00:06:12,000 --> 00:06:13,980 and the code is accessing the player class 133 00:06:13,980 --> 00:06:17,080 data attributes directly to print them out 134 00:06:17,080 --> 00:06:18,840 or alter their values. 135 00:06:18,840 --> 00:06:22,100 Now the attributes such as lives and names 136 00:06:22,100 --> 00:06:24,700 are encapsulated in the player class, 137 00:06:24,700 --> 00:06:26,180 but they're not hidden 138 00:06:26,180 --> 00:06:30,460 and that's something that I'm sure Java and C++ programmers 139 00:06:30,460 --> 00:06:33,540 will find horrible because in those languages, 140 00:06:33,540 --> 00:06:35,910 providing direct access to the data attributes 141 00:06:35,910 --> 00:06:38,710 is really frowned upon but in Python, 142 00:06:38,710 --> 00:06:40,130 it's considered the opposite, 143 00:06:40,130 --> 00:06:42,670 in other words the way to do things. 144 00:06:42,670 --> 00:06:45,140 So the first thing I'm gonna say about getters and setters 145 00:06:45,140 --> 00:06:48,150 in Python is don't use them. 146 00:06:48,150 --> 00:06:50,220 And I guess that's probably a strange thing to say 147 00:06:50,220 --> 00:06:53,250 in a video about using getters and setters in Python 148 00:06:53,250 --> 00:06:56,200 so I better explain that I don't mean never use them, 149 00:06:56,200 --> 00:06:58,070 I mean don't worry about them 150 00:06:58,070 --> 00:07:00,170 when you're creating your classes 151 00:07:00,170 --> 00:07:02,800 and that's because chances are you won't need them 152 00:07:02,800 --> 00:07:05,500 so don't spend time creating getters and setters 153 00:07:05,500 --> 00:07:08,000 that won't be needed. 154 00:07:08,000 --> 00:07:12,830 Now in Python, you can add a getter or a setter or both 155 00:07:12,830 --> 00:07:16,480 after you created your class and any code using the class 156 00:07:16,480 --> 00:07:18,440 will continue to work fine, 157 00:07:18,440 --> 00:07:21,720 but in Java or C++ that's not possible. 158 00:07:21,720 --> 00:07:25,470 If you allow access to class instance variables later 159 00:07:25,470 --> 00:07:27,210 to start to make them private, 160 00:07:27,210 --> 00:07:30,090 any code that uses the class will have to be changed 161 00:07:30,090 --> 00:07:32,640 to use the getters and setters instead. 162 00:07:32,640 --> 00:07:35,090 As we see in Python though, client code, 163 00:07:35,090 --> 00:07:38,710 that's code that is using the class, isn't affected. 164 00:07:38,710 --> 00:07:41,420 All right, so what are these getters and setters? 165 00:07:41,420 --> 00:07:43,290 Well, a getter is actually a method 166 00:07:43,290 --> 00:07:47,270 that's used to get the value of a data attribute. 167 00:07:47,270 --> 00:07:50,580 So as an example, if we look at the code on line five, 168 00:07:50,580 --> 00:07:52,070 it's actually printing out 169 00:07:52,070 --> 00:07:55,320 the data attribute directly, tim.name, 170 00:07:55,320 --> 00:07:57,160 so instead of that if we wanted to access a name, 171 00:07:57,160 --> 00:07:59,480 we might come down and do something like this, 172 00:07:59,480 --> 00:08:02,650 print tim.get underscore name like so. 173 00:08:07,280 --> 00:08:10,970 So the get underscore name method is called a getter 174 00:08:10,970 --> 00:08:12,740 and normally it just returns the value 175 00:08:12,740 --> 00:08:14,810 of the corresponding variable, 176 00:08:14,810 --> 00:08:16,480 but it can actually do more than that. 177 00:08:16,480 --> 00:08:18,490 For example, the getter for the score 178 00:08:18,490 --> 00:08:21,620 could multiply the score by perhaps the number of lives. 179 00:08:21,620 --> 00:08:23,930 That way, a player's score is much higher 180 00:08:23,930 --> 00:08:27,180 if they've completed the game without losing too many lives. 181 00:08:27,180 --> 00:08:28,850 So getters can be useful 182 00:08:28,850 --> 00:08:30,950 and you'll want to add them sometimes, 183 00:08:30,950 --> 00:08:31,970 but the point I'm making 184 00:08:31,970 --> 00:08:33,510 is that you can add them to the class 185 00:08:33,510 --> 00:08:35,320 if you later decide you need them, 186 00:08:35,320 --> 00:08:36,940 but there's no point in creating them 187 00:08:36,940 --> 00:08:38,330 just for the sake of it 188 00:08:38,330 --> 00:08:41,320 or just because you've come to Python from another language 189 00:08:41,320 --> 00:08:42,860 where you have to use a getter 190 00:08:42,860 --> 00:08:45,390 if you think there might be the faintest possibility 191 00:08:45,390 --> 00:08:47,400 that you'll need one in the future. 192 00:08:47,400 --> 00:08:49,090 All right, so that's the getter, 193 00:08:49,090 --> 00:08:50,810 but a setter is just a method 194 00:08:50,810 --> 00:08:53,650 that's used to set the value of the class data attribute 195 00:08:53,650 --> 00:08:55,560 and it might look something like this, 196 00:08:55,560 --> 00:08:57,970 tim.set underscore lives 300. 197 00:09:01,340 --> 00:09:03,930 A setter may be useful for the lives attribute 198 00:09:03,930 --> 00:09:05,700 of our player class. 199 00:09:05,700 --> 00:09:07,680 It doesn't make sense for the number of lives 200 00:09:07,680 --> 00:09:11,130 to drop below zero so using a setter is a good way 201 00:09:11,130 --> 00:09:14,450 to check the value before updating the attribute. 202 00:09:14,450 --> 00:09:17,800 Now these two examples on line 10 and 11 203 00:09:17,800 --> 00:09:20,880 are how you would use a getter and setter in Java 204 00:09:20,880 --> 00:09:23,660 or C++ for example but in Python, 205 00:09:23,660 --> 00:09:26,380 they actually work a bit differently. 206 00:09:26,380 --> 00:09:28,380 Now the basic principle is the same, 207 00:09:28,380 --> 00:09:32,280 that is to use a method to return the value of an attribute 208 00:09:32,280 --> 00:09:33,990 or assign a new value to it, 209 00:09:33,990 --> 00:09:35,980 but you still use the same syntax 210 00:09:35,980 --> 00:09:39,540 as you would when accessing the attributes directly. 211 00:09:39,540 --> 00:09:42,290 I'm gonna delete these two lines. 212 00:09:45,640 --> 00:09:47,970 Let's go ahead and add a getter and setter 213 00:09:47,970 --> 00:09:50,930 for our lives attribute in the player class. 214 00:09:50,930 --> 00:09:53,650 All right, so going back to the player.py file, 215 00:09:53,650 --> 00:09:57,310 so the first thing we wanna do is hide our lives attribute 216 00:09:57,310 --> 00:09:59,980 by prefixing it with an underscore. 217 00:09:59,980 --> 00:10:02,190 I'm talking about the code here on line five. 218 00:10:02,190 --> 00:10:06,690 So it's gonna be self. and put an underscore there 219 00:10:06,690 --> 00:10:09,260 for underscore lives equals three. 220 00:10:09,260 --> 00:10:10,720 So once we've done that, 221 00:10:10,720 --> 00:10:14,160 we need to create a method to set the value to setter 222 00:10:14,160 --> 00:10:16,990 and of course another method to get the value to getter. 223 00:10:16,990 --> 00:10:19,690 Let's go ahead and do both of those. 224 00:10:19,690 --> 00:10:21,520 So we'll start with the getter 225 00:10:21,520 --> 00:10:25,690 so that's gonna be def space underscore get underscore lives 226 00:10:27,920 --> 00:10:31,670 self colon and return self. underscore lives. 227 00:10:35,560 --> 00:10:40,390 Then we'll do a def underscore set underscore lives 228 00:10:40,390 --> 00:10:41,680 and self in parenthesis 229 00:10:41,680 --> 00:10:43,770 which is added automatically by IntelliJ 230 00:10:43,770 --> 00:10:47,480 and then we're gonna do self. underscore lives 231 00:10:47,480 --> 00:10:48,980 is equal to lives. 232 00:10:50,540 --> 00:10:52,690 And the other thing I'll need to do here is add a parameter 233 00:10:52,690 --> 00:10:54,110 because it's the set method. 234 00:10:54,110 --> 00:10:57,010 We need to pass the number of lives we wanna set it to 235 00:10:57,010 --> 00:10:57,960 and that's it. 236 00:10:57,960 --> 00:10:59,830 Now once again, we're hiding these methods 237 00:10:59,830 --> 00:11:02,580 by starting their names with an underscore. 238 00:11:02,580 --> 00:11:04,930 Of course, they're not really hidden as such, 239 00:11:04,930 --> 00:11:07,480 but there's no need for clients to use them directly 240 00:11:07,480 --> 00:11:09,810 and the underscore at the start of the name 241 00:11:09,810 --> 00:11:12,540 gives users of our class an indication 242 00:11:12,540 --> 00:11:15,960 that they shouldn't really be calling these methods. 243 00:11:15,960 --> 00:11:17,870 Okay, so the last step now 244 00:11:17,870 --> 00:11:20,350 is to define a property called lives 245 00:11:20,350 --> 00:11:22,130 that uses these two methods 246 00:11:22,130 --> 00:11:25,240 when reading and writing our lives attribute. 247 00:11:25,240 --> 00:11:27,280 All right, so let's actually add that now. 248 00:11:27,280 --> 00:11:30,280 So we put lives is equal to property 249 00:11:32,760 --> 00:11:36,390 and it's going to be underscore get underscore lives 250 00:11:36,390 --> 00:11:37,890 without the parenthesis 251 00:11:37,890 --> 00:11:40,580 and underscore set underscore lives 252 00:11:40,580 --> 00:11:43,150 again without any parenthesis. 253 00:11:43,150 --> 00:11:46,440 So our data attribute is now called underscore lives 254 00:11:46,440 --> 00:11:49,590 and we've replaced it with a property called lives 255 00:11:49,590 --> 00:11:53,480 that uses these two methods to access the number of lives 256 00:11:53,480 --> 00:11:55,180 that the player has. 257 00:11:55,180 --> 00:11:58,810 Now back in main.py, if I go back over there, 258 00:11:58,810 --> 00:12:00,310 I can run the programme as is 259 00:12:00,310 --> 00:12:02,860 and everything should still work. 260 00:12:02,860 --> 00:12:05,280 We get the same results as we got previously. 261 00:12:05,280 --> 00:12:07,210 Tim starts off with three lives 262 00:12:07,210 --> 00:12:09,890 which we've printed out on line six. 263 00:12:09,890 --> 00:12:13,430 Then there's two left after we subtract one on line seven 264 00:12:13,430 --> 00:12:15,170 and obviously we're printing out the results of that 265 00:12:15,170 --> 00:12:16,510 on line eight. 266 00:12:16,510 --> 00:12:19,040 So I haven't actually had to make any changes 267 00:12:19,040 --> 00:12:20,610 to our main programme 268 00:12:20,610 --> 00:12:23,120 so it continues to use the player class 269 00:12:23,120 --> 00:12:24,890 in exactly the same way as it did 270 00:12:24,890 --> 00:12:27,420 before we changed the lives attribute 271 00:12:27,420 --> 00:12:29,720 to use the getter and setter methods. 272 00:12:29,720 --> 00:12:30,820 But now that we've done this, 273 00:12:30,820 --> 00:12:33,560 we can add some validation to the setter method 274 00:12:33,560 --> 00:12:36,940 to prevent the number of lives from dropping below zero. 275 00:12:36,940 --> 00:12:40,500 So going back to our player class in the setter method, 276 00:12:40,500 --> 00:12:44,410 we could add some code to do that validation 277 00:12:44,410 --> 00:12:47,450 so we could put if space lives 278 00:12:47,450 --> 00:12:50,780 is greater than or equal to zero colon 279 00:12:50,780 --> 00:12:55,300 then we'll put our self. underscore lives equals lives 280 00:12:55,300 --> 00:12:57,820 then we'll add an else clause else 281 00:12:57,820 --> 00:13:01,820 and we've got our print lives cannot be negative 282 00:13:04,490 --> 00:13:08,100 and self. underscore lives equals zero. 283 00:13:08,100 --> 00:13:09,700 All right, so that's the validation 284 00:13:09,700 --> 00:13:11,000 that only effectively allows us 285 00:13:11,000 --> 00:13:13,610 to set the value of the lives variable, 286 00:13:13,610 --> 00:13:15,120 underscore lives variable, 287 00:13:15,120 --> 00:13:18,560 if the values passed is greater than or equal to zero. 288 00:13:18,560 --> 00:13:20,080 And if that's not the case, 289 00:13:20,080 --> 00:13:22,930 then we print out the message lives cannot be negative 290 00:13:22,930 --> 00:13:25,430 and then we set underscore lives to zero. 291 00:13:25,430 --> 00:13:26,830 So while I'm here, 292 00:13:26,830 --> 00:13:28,220 I'm gonna add a method that we can use 293 00:13:28,220 --> 00:13:30,250 to print out the values of the attributes 294 00:13:30,250 --> 00:13:31,270 so let's go ahead and do that. 295 00:13:31,270 --> 00:13:35,150 We'll put that below the lives property line. 296 00:13:35,150 --> 00:13:39,320 We def space underscore underscore str underscore underscore 297 00:13:42,290 --> 00:13:45,080 and we add the self which added automatically by IntelliJ 298 00:13:45,080 --> 00:13:46,500 then let's return 299 00:13:47,600 --> 00:13:50,100 name and curly brace zero.name 300 00:13:53,460 --> 00:13:54,790 lives zero.lives 301 00:13:59,630 --> 00:14:00,970 level zero.level 302 00:14:05,200 --> 00:14:07,540 and finally score zero.score 303 00:14:10,060 --> 00:14:12,940 and at the end of that line after the double quote, 304 00:14:12,940 --> 00:14:14,020 .format self. 305 00:14:15,630 --> 00:14:16,890 So when you print an object, 306 00:14:16,890 --> 00:14:18,740 Python looks for a special method 307 00:14:18,740 --> 00:14:22,240 called underscore underscore str underscore underscore 308 00:14:22,240 --> 00:14:24,410 which we've just defined on line 21 309 00:14:24,410 --> 00:14:25,520 and I'm gonna call that method 310 00:14:25,520 --> 00:14:28,460 when it needs a string representation of the object 311 00:14:28,460 --> 00:14:30,750 such as when you wanna print it. 312 00:14:30,750 --> 00:14:32,280 Now I've created this method 313 00:14:32,280 --> 00:14:35,130 so that we can easily see the values of the attributes 314 00:14:35,130 --> 00:14:36,800 and I'll come back to that strange use 315 00:14:36,800 --> 00:14:39,300 of the replacement field shortly. 316 00:14:39,300 --> 00:14:42,020 Okay, so we've added some code to the lives setter 317 00:14:42,020 --> 00:14:44,160 to prevent the number of lives going negative 318 00:14:44,160 --> 00:14:45,470 so let's test this. 319 00:14:45,470 --> 00:14:48,280 So we're going back to the main programme 320 00:14:48,280 --> 00:14:52,650 and let's copy lines seven and eight three more times 321 00:14:52,650 --> 00:14:54,850 so I'm gonna copy those 322 00:14:54,850 --> 00:14:58,890 and let's put them outside there, there and three 323 00:14:58,890 --> 00:15:00,200 as you can see. 324 00:15:00,200 --> 00:15:02,590 So we're reducing the value of lives by one each time 325 00:15:02,590 --> 00:15:03,930 and printing out the value 326 00:15:03,930 --> 00:15:05,850 until we get down to the last value 327 00:15:05,850 --> 00:15:08,130 which hopefully is going to be hitting zero, 328 00:15:08,130 --> 00:15:09,250 but the other thing I probably should have done 329 00:15:09,250 --> 00:15:11,170 before I copied it was change this 330 00:15:11,170 --> 00:15:13,110 so instead of just printing out lives, 331 00:15:13,110 --> 00:15:15,550 it prints out just tim. 332 00:15:15,550 --> 00:15:16,430 And now that we've created 333 00:15:16,430 --> 00:15:19,200 that underscore underscore str function, 334 00:15:19,200 --> 00:15:23,480 let's take advantage of that, okay, like so. 335 00:15:23,480 --> 00:15:27,000 So let's run this now and see if it works. 336 00:15:27,000 --> 00:15:27,880 All right, so you can see there 337 00:15:27,880 --> 00:15:31,620 that we've got our lives getting reduced each time we call 338 00:15:31,620 --> 00:15:33,370 and then once it gets to below zero 339 00:15:33,370 --> 00:15:34,860 or would have gone below zero, 340 00:15:34,860 --> 00:15:37,480 we see that we got a message lives cannot be negative 341 00:15:37,480 --> 00:15:40,780 and the number of lives remains at zero. 342 00:15:40,780 --> 00:15:43,580 So although setters aren't needed as such in Python, 343 00:15:43,580 --> 00:15:46,430 they're very useful when you'd want to include validation 344 00:15:46,430 --> 00:15:50,380 on the values that your data attributes can be set to. 345 00:15:50,380 --> 00:15:52,060 All right, so I've skimmed over a couple of things 346 00:15:52,060 --> 00:15:54,700 that we've done in the player class so in the next video, 347 00:15:54,700 --> 00:15:57,100 let's have a look at those things in a bit more detail. 348 00:15:57,100 --> 00:15:59,280 I'll see you in the next video.