1
00:00:05,380 --> 00:00:08,520
Welcome back to part two of our discussion of object oriented programming.

2
00:00:08,620 --> 00:00:11,080
Well we're going to talk about methods and inheritance.

3
00:00:11,080 --> 00:00:13,820
Let's head back to text editor where we left off last time.

4
00:00:14,020 --> 00:00:18,310
Last time we left off at creating this dog class that only had attributes.

5
00:00:18,310 --> 00:00:22,990
And we also discussed class object attributes which are attributes which are going to be true for any

6
00:00:22,990 --> 00:00:24,950
instance of the stock object.

7
00:00:24,970 --> 00:00:29,410
So it doesn't matter what kind of breed or name the stock can have or it also doesn't matter if we create

8
00:00:29,410 --> 00:00:30,390
a brand new dog.

9
00:00:30,520 --> 00:00:35,050
So I can create a variable called new dog which is also an instance of the dog class.

10
00:00:35,080 --> 00:00:41,900
This one may be a golden retriever so say Golden is the breed and the name will just have this dog.

11
00:00:41,920 --> 00:00:52,550
Cindy and if I say Prince new dog species save I'll get back mammal as well.

12
00:00:52,590 --> 00:00:53,730
So I get mammal mammal.

13
00:00:53,770 --> 00:00:58,350
Doesn't matter what the breed instance or name of the dog is this class object attribute is going to

14
00:00:58,350 --> 00:00:59,860
be the same for all of them.

15
00:00:59,910 --> 00:01:05,760
So let's now talk about methods which are basically going to be actions you perform on the object.

16
00:01:06,090 --> 00:01:10,290
So I'm going to delete all this code and let's start with something new.

17
00:01:10,290 --> 00:01:15,620
We're going to create a circle class and we'll say DMF.

18
00:01:15,630 --> 00:01:17,150
Let me zoom in here just a little bit.

19
00:01:18,800 --> 00:01:21,700
We'll say T.F. and we create our own method.

20
00:01:21,710 --> 00:01:28,780
Remember this is double underscores so underscore underscore and we'll say self and in this case we're

21
00:01:28,780 --> 00:01:34,100
going to define an attribute as radius and we can also give a default value just like we could for a

22
00:01:34,100 --> 00:01:35,000
normal function.

23
00:01:35,000 --> 00:01:41,540
I'll say radious by default is equal to 1 in case the user doesn't provide it then we'll say sulf thought

24
00:01:41,540 --> 00:01:45,790
radius is equal to radius OK.

25
00:01:46,070 --> 00:01:47,390
So we have class circle.

26
00:01:47,400 --> 00:01:52,850
And in this method when you create a new instance of the circle class you can provide a radius for it.

27
00:01:52,850 --> 00:01:57,650
If you don't provide a radius then the default will just be radius equal to 1.

28
00:01:57,710 --> 00:02:03,810
So let's create an instance of it will say My circle is equal to in its circle.

29
00:02:04,360 --> 00:02:08,350
And then I'll print how my circles radius.

30
00:02:08,900 --> 00:02:10,410
Let's run this.

31
00:02:10,550 --> 00:02:16,800
And now I get back 1 as a radius that circle however I could provide in my own radius such as 10.

32
00:02:17,030 --> 00:02:18,080
And when I run this again.

33
00:02:18,300 --> 00:02:23,030
Now I get back 10 so I have this default radius which you can always overwrite when I'm creating a new

34
00:02:23,030 --> 00:02:25,090
instance of my circle.

35
00:02:25,100 --> 00:02:29,210
Now think of a class object attribute which is going to be true for any circle.

36
00:02:29,690 --> 00:02:31,190
One of these could be pi.

37
00:02:31,580 --> 00:02:37,460
So the value of pi or that ratio 3.1 for that's going to be pretty much true for any circle regardless

38
00:02:37,460 --> 00:02:38,310
of the radius.

39
00:02:38,330 --> 00:02:44,460
So it could set that as a class object attribute though the second house under that init method.

40
00:02:45,970 --> 00:02:49,310
So far we've only discussed attributes now discuss methods.

41
00:02:49,450 --> 00:02:53,170
So this init method is technically what's known as a special method.

42
00:02:53,170 --> 00:02:55,550
Again it has that double set of underscores to show you that.

43
00:02:55,710 --> 00:03:01,660
But you can create your own methods that performs some sort of action with or on the object.

44
00:03:01,720 --> 00:03:09,410
So let's create a method for calculating area and by default every method should start first with self.

45
00:03:09,480 --> 00:03:14,970
Basically that tells Python that you're referring to the instance of the object you create when applying

46
00:03:15,030 --> 00:03:16,760
this particular method.

47
00:03:16,920 --> 00:03:23,520
So area is just going to return the area of the circle which in this case is pi r squared.

48
00:03:23,520 --> 00:03:32,310
So we're going to say self-taught radius times self-taught radius times self-taught pi.

49
00:03:32,950 --> 00:03:41,450
So it saved that and I will say my circle radius and then we'll print out my circle area.

50
00:03:41,660 --> 00:03:43,090
But notice what happens.

51
00:03:43,130 --> 00:03:49,190
Area itself is a method which means if I just called that area it's actually not going to execute the

52
00:03:49,190 --> 00:03:50,270
method.

53
00:03:50,420 --> 00:03:51,670
Self-taught radius.

54
00:03:51,680 --> 00:03:52,790
That's an attribute.

55
00:03:52,970 --> 00:03:56,370
But this DPF area is going to be a method that you can tell.

56
00:03:56,390 --> 00:04:00,410
It's a method because it has DPF in front of it very much like a function would.

57
00:04:00,770 --> 00:04:02,740
So let's say this and run it and see what happens.

58
00:04:04,000 --> 00:04:06,340
Right now I get 10 for the radius.

59
00:04:06,340 --> 00:04:12,580
But when I call my circle the area I get this bound Methot Circle area of main circle object at this

60
00:04:12,580 --> 00:04:18,250
location memory and very similar to what we are working on functions in order to execute a method.

61
00:04:18,250 --> 00:04:23,240
You have to have the open and close princes and then you can see the syntax highlighting has even changed.

62
00:04:23,290 --> 00:04:30,820
Now when I run this I'm able to see the actual area of the circle three fourteen point zero so are squared

63
00:04:30,970 --> 00:04:32,350
times pi.

64
00:04:32,470 --> 00:04:33,130
OK.

65
00:04:33,160 --> 00:04:39,460
So again the method is going to perform an action and it can return or it can actually affect the object

66
00:04:39,460 --> 00:04:41,680
itself without returning anything.

67
00:04:41,680 --> 00:04:44,290
Just keep that in mind for future reference.

68
00:04:45,270 --> 00:04:52,880
Let's try adding a new method which calculates the circumference of a circle will say the F will say

69
00:04:53,370 --> 00:04:54,940
circumference.

70
00:04:55,320 --> 00:05:03,840
We pass and self and then we'll say return and circumference of a circle is 2 times pi.

71
00:05:03,850 --> 00:05:09,640
So we'll say self-taught pi times the radius which in this case is self-taught radius.

72
00:05:09,640 --> 00:05:14,390
Notice here how I'm saying self-taught radius instead of just radius.

73
00:05:14,410 --> 00:05:18,840
If I say just radius Pi does not understand what I'm referring to.

74
00:05:18,910 --> 00:05:19,720
I need to tell it.

75
00:05:19,720 --> 00:05:24,660
Hey I'm talking about self-taught radius the radius of the circle that it was assigned upon create in

76
00:05:24,660 --> 00:05:25,760
the circle.

77
00:05:26,280 --> 00:05:28,400
So a self-taught radius there.

78
00:05:28,720 --> 00:05:32,190
Let's run this and whoops we actually forgot to execute it.

79
00:05:32,200 --> 00:05:38,620
So let's come back here and say my circle circumference again remember those open close Princie so we

80
00:05:38,620 --> 00:05:40,680
can actually run this method.

81
00:05:40,720 --> 00:05:46,300
I run this and I see the circumference of the circle with some extra precision due to using floating

82
00:05:46,300 --> 00:05:48,770
point numbers appear OK.

83
00:05:49,050 --> 00:05:53,470
So we were able to create our own methods for area and circumference.

84
00:05:53,490 --> 00:05:56,130
The next thing I want to talk about is inheritance.

85
00:05:56,460 --> 00:05:58,800
So I'm going to clear these examples.

86
00:06:01,200 --> 00:06:09,800
And let's create a class called animal it's going to be a very simple class it's going to have an in

87
00:06:09,810 --> 00:06:10,470
it method.

88
00:06:12,020 --> 00:06:14,700
With self it's not going to take any other parameters.

89
00:06:14,960 --> 00:06:17,440
And in this case we're not even going to assign any attributes.

90
00:06:17,440 --> 00:06:28,690
We're just going to say animal created then we're going to say T.F. report self and this will be a method

91
00:06:29,380 --> 00:06:44,200
that just prints out animal then we're going to create one more method self that prints out eating.

92
00:06:44,240 --> 00:06:46,220
OK so let's play around with this.

93
00:06:46,220 --> 00:06:49,780
I'm going to create an instance of my animal object.

94
00:06:49,820 --> 00:06:58,040
So say a is equal to an animal object and then we'll say a dot and let's have it eats and let's have

95
00:06:58,040 --> 00:07:00,320
it report.

96
00:07:00,320 --> 00:07:05,630
Notice tone after call print on eata report because those methods themselves already print out for me

97
00:07:06,770 --> 00:07:11,930
and I'm going to zoom out a little bit so we can see the whole class on the screen.

98
00:07:11,930 --> 00:07:13,190
So let's run this.

99
00:07:13,430 --> 00:07:14,820
And notice I get back.

100
00:07:15,020 --> 00:07:17,060
Eating an animal.

101
00:07:17,360 --> 00:07:17,850
OK.

102
00:07:18,050 --> 00:07:20,450
So pretty basic class right here.

103
00:07:20,550 --> 00:07:25,040
Again it's just going to print's animal created upon creating an animal or animal created that happens

104
00:07:25,040 --> 00:07:25,930
on line 12.

105
00:07:26,030 --> 00:07:29,190
Then it says eating and that it's an animal.

106
00:07:29,200 --> 00:07:38,370
Now maybe you want to create a new class such as a dog class and you start thinking to yourself Hey

107
00:07:38,370 --> 00:07:42,220
I already did all this work with the Animal class maybe I could reduce some of this.

108
00:07:42,240 --> 00:07:47,550
For example I would like dogs to have an eat method and have them say that they're eating.

109
00:07:47,610 --> 00:07:53,100
So how can actually take advantage of all the prior work that I've done on the Animal class with my

110
00:07:53,250 --> 00:07:59,540
dog class which you can do is you can inherit the Animal class and the way you do this is you just pass

111
00:07:59,540 --> 00:08:07,110
an animal no princes as far as the end of the animal into the dog class and then inside of that class

112
00:08:07,620 --> 00:08:22,920
you're going to say in its self and then here you can say Prince dog created save that and now down

113
00:08:22,920 --> 00:08:28,070
here what I'm going to do is I'm going to create an instance of the class so I'll say D.

114
00:08:28,350 --> 00:08:33,190
Is equal to dog.

115
00:08:33,330 --> 00:08:39,570
But then what I'm going to do is inside this method for dog I'm going to initialize the animal method

116
00:08:39,600 --> 00:08:49,750
I inherited Saussy animal dot underscore underscore that underscore underscore and then passen self

117
00:08:50,660 --> 00:08:57,080
so what this says is upon creating an instance of dog I'm going to using my inheritance from animal

118
00:08:57,440 --> 00:09:01,410
create an instance of the Animal class and then print that created.

119
00:09:01,460 --> 00:09:06,840
So when I create dog here I should see animal created because I'm calling in it down here an animal.

120
00:09:06,890 --> 00:09:08,700
And then I should see dog created.

121
00:09:08,720 --> 00:09:10,100
Let's see if that happens.

122
00:09:11,790 --> 00:09:15,810
So I scroll up and there we have it animal created and dog created.

123
00:09:15,810 --> 00:09:21,820
Now the question arises there are these other useful methods on animal report and eat.

124
00:09:22,200 --> 00:09:25,620
Let's see if now I have access to them from the dog class.

125
00:09:25,910 --> 00:09:27,510
So I'm going to say D.

126
00:09:27,570 --> 00:09:29,100
Eat notice here.

127
00:09:29,160 --> 00:09:32,510
I never defined eat inside of my thought class.

128
00:09:32,580 --> 00:09:36,250
It's only the inside of the Animal class.

129
00:09:36,350 --> 00:09:42,710
I'm going to run this and I get back eating even though I never strictly defined it inside of the dog

130
00:09:42,710 --> 00:09:43,270
class.

131
00:09:43,290 --> 00:09:51,060
I was able to inherit that method of eat from the Animal class and this is what inheritance all about

132
00:09:51,240 --> 00:09:58,200
being able to use methods or attributes that you already defined in another class with a new class.

133
00:09:58,200 --> 00:10:01,640
So now I have access to eat and I should also have access to report.

134
00:10:01,980 --> 00:10:10,990
So Saidy report run this and now I get to see dog created eating an animal.

135
00:10:11,230 --> 00:10:13,100
However let's think about this.

136
00:10:13,120 --> 00:10:16,060
Maybe I want to be more specific in my report than just animal.

137
00:10:16,090 --> 00:10:18,340
Maybe they would like it to report dog.

138
00:10:18,610 --> 00:10:20,080
Well that's no problem.

139
00:10:20,080 --> 00:10:22,730
We can easily overwrite inherited methods.

140
00:10:22,870 --> 00:10:29,810
All I need to say is the earth choose the same method name report say self.

141
00:10:29,810 --> 00:10:31,540
And then it's going to print.

142
00:10:32,120 --> 00:10:41,180
I am a dog so now when you call report even though you're inheriting from animal and animal typically

143
00:10:41,180 --> 00:10:43,350
prints animal for its report.

144
00:10:43,460 --> 00:10:46,570
Now Dog overwrote that and now it's going to print.

145
00:10:46,640 --> 00:10:48,920
I am a dog.

146
00:10:48,920 --> 00:10:54,230
So when I run this python in my example it's going to say dog created right above it.

147
00:10:54,290 --> 00:10:55,200
Animal created.

148
00:10:55,400 --> 00:10:58,050
That comes from this line and it Methot off animal.

149
00:10:58,130 --> 00:11:03,860
Then it says Dog created that comes from this line print dog created and then when you call dog eats

150
00:11:04,370 --> 00:11:07,660
that's actually calling the inheritance method here eating.

151
00:11:07,760 --> 00:11:11,990
And then when you call I am a dog off report.

152
00:11:12,130 --> 00:11:13,890
That's this report Prince.

153
00:11:13,920 --> 00:11:14,610
I am a dog.

154
00:11:14,610 --> 00:11:19,860
You were able to successfully overwrite this old report method that you inherited from and that's the

155
00:11:19,860 --> 00:11:25,820
basic idea behind inheritance being able to use old methods from another class to find.

156
00:11:25,920 --> 00:11:29,840
And then if you ever want to you can always overwrite those methods yourself.

157
00:11:29,850 --> 00:11:37,070
Now something I'm often asked is What do you do if your animal init method actually took attributes.

158
00:11:37,350 --> 00:11:44,300
So for example let's say the animals had a fur attribute so so me delete this print statement and say

159
00:11:44,840 --> 00:11:50,890
self-taught for is equal to the fur provided in this case.

160
00:11:50,910 --> 00:11:57,240
If I were to try to run this I would get back an error it would say hey this is missing one required

161
00:11:57,240 --> 00:12:02,230
positional argument for and that's coming from this animal in itself line.

162
00:12:02,280 --> 00:12:09,050
So right here it's saying hey animals you're required to say what kind of fur this animal has.

163
00:12:09,180 --> 00:12:13,650
And when you created in the heritage from the instance of the class down here when you're saying D is

164
00:12:13,650 --> 00:12:14,430
equal to dog.

165
00:12:14,640 --> 00:12:16,880
You forgot to provide what fur.

166
00:12:17,040 --> 00:12:18,090
Well that's no problem.

167
00:12:18,090 --> 00:12:26,490
All you need to do is then accept a parameter for the init method of your dog class and then stick that

168
00:12:26,490 --> 00:12:31,410
for parameter into the method of the animal call.

169
00:12:31,990 --> 00:12:37,530
And I want to save this if I just read this right now still get an error because it saying hey you're

170
00:12:37,530 --> 00:12:42,030
forgetting to provide for so on it to do inside the class is provided for.

171
00:12:42,030 --> 00:12:48,450
So maybe I'll say this dog has fuzzy for an hour when you run it you don't get an error it just says

172
00:12:48,450 --> 00:12:50,360
Dog created eating and I am a dog.

173
00:12:50,580 --> 00:12:59,010
And if we delete all these I can always say d dot for and I can print out type notice again that first

174
00:12:59,010 --> 00:13:00,500
an attribute in this case.

175
00:13:00,500 --> 00:13:07,790
So I run this and you get back dog created fuzzy and notice it's no longer printing animal created because

176
00:13:07,790 --> 00:13:08,220
I don't know.

177
00:13:08,240 --> 00:13:11,480
No longer have that print statement there in the animal.

178
00:13:11,480 --> 00:13:17,990
So instead I'm saying in it except for assigns that for and if I ever need to do that with my inherited

179
00:13:17,990 --> 00:13:24,020
class I can just pasan in its own init method and then pass that into the inherited class method.

180
00:13:24,480 --> 00:13:24,950
OK.

181
00:13:25,160 --> 00:13:27,790
That's the very basics of methods and inheritance.

182
00:13:27,950 --> 00:13:33,290
Remember methods are essentially functions defined inside the body of a class and they're used to perform

183
00:13:33,350 --> 00:13:40,360
operations with the attributes of our objects inheritance is a way to form new classes using classes

184
00:13:40,360 --> 00:13:45,760
that have already been defined and those newly formed classes are called derived classes and the classes

185
00:13:45,760 --> 00:13:48,130
that we derive from are called base classes.

186
00:13:48,130 --> 00:13:53,950
So in this case animals the base class in dogs the derived class if you have any questions feel free

187
00:13:53,950 --> 00:13:55,410
to post to Cunanan forums.

188
00:13:55,420 --> 00:14:00,670
We have one lecturer left in this O.P. series which is just special methods essentially methods that

189
00:14:00,670 --> 00:14:03,720
allow us to interact with built in Python functions.

190
00:14:03,790 --> 00:14:04,420
We'll see if they're.