WEBVTT

1
00:00:01.189 --> 00:00:03.830
so at the end of the last video we

2
00:00:03.830 --> 00:00:06.200
created troll class which if you recall
so at the end of the last video we

3
00:00:06.200 --> 00:00:09.679
was a subclass of enemy at the moment
created troll class which if you recall

4
00:00:09.679 --> 00:00:11.629
it's not doing anything useful as you
was a subclass of enemy at the moment

5
00:00:11.629 --> 00:00:13.519
saw we could just as easily use an enemy
it's not doing anything useful as you

6
00:00:13.519 --> 00:00:16.039
instead and get exactly the same result
saw we could just as easily use an enemy

7
00:00:16.039 --> 00:00:19.010
so inspired by his brothers fine example
instead and get exactly the same result

8
00:00:19.010 --> 00:00:22.010
ugs game or has been going to the gym and
so inspired by his brothers fine example

9
00:00:22.010 --> 00:00:24.440
working out in fact he's still a bit of
ugs game or has been going to the gym and

10
00:00:24.440 --> 00:00:26.630
a trend and now all the trolls have
working out in fact he's still a bit of

11
00:00:26.630 --> 00:00:29.270
been toughened up so every trolls that
a trend and now all the trolls have

12
00:00:29.270 --> 00:00:31.280
our adventurers encounter in this game
been toughened up so every trolls that

13
00:00:31.280 --> 00:00:35.300
will now take 23 points of damage now
our adventurers encounter in this game

14
00:00:35.300 --> 00:00:37.010
because they're mortal only have one
will now take 23 points of damage now

15
00:00:37.010 --> 00:00:39.199
life so there's no need to specify
because they're mortal only have one

16
00:00:39.199 --> 00:00:42.140
either value when we create them what we
life so there's no need to specify

17
00:00:42.140 --> 00:00:44.210
need to do is initialize the troll
either value when we create them what we

18
00:00:44.210 --> 00:00:46.609
instances with just a name so that we
need to do is initialize the troll

19
00:00:46.609 --> 00:00:48.979
can tell them apart the hit points and
instances with just a name so that we

20
00:00:48.979 --> 00:00:50.870
lives will be the same for every troll
can tell them apart the hit points and

21
00:00:50.870 --> 00:00:54.199
that we create so going back to our
lives will be the same for every troll

22
00:00:54.199 --> 00:00:57.079
enemy class where our trolls are defined
that we create so going back to our

23
00:00:57.079 --> 00:01:00.260
at the moment we just got pass in their so
enemy class where our trolls are defined

24
00:01:00.260 --> 00:01:01.219
we're going to change that we're going
at the moment we just got pass in their so

25
00:01:01.219 --> 00:01:03.859
to actually delete that and then we're
we're going to change that we're going

26
00:01:03.859 --> 00:01:05.870
going to come down here we're going to
to actually delete that and then we're

27
00:01:05.870 --> 00:01:09.800
add our init....
going to come down here we're going to

28
00:01:09.800 --> 00:01:12.260
....
add our init....

29
00:01:12.260 --> 00:01:14.870
....
....

30
00:01:14.870 --> 00:01:19.220
...
....

31
00:01:19.220 --> 00:01:22.820
...
...

32
00:01:22.820 --> 00:01:24.260
so the hit points and lives will be the same
...

33
00:01:24.260 --> 00:01:26.660
for every troll we create the name the
so the hit points and lives will be the same

34
00:01:26.660 --> 00:01:28.130
instance rather is just going to have a
for every troll we create the name the

35
00:01:28.130 --> 00:01:30.260
name and that's why we're passing it as
instance rather is just going to have a

36
00:01:30.260 --> 00:01:32.090
a parameter to the constructor to the
name and that's why we're passing it as

37
00:01:32.090 --> 00:01:34.190
init method the underscore underscore init
a parameter to the constructor to the

38
00:01:34.190 --> 00:01:34.760
init method the underscore underscore init

39
00:01:34.760 --> 00:01:36.710
__ which all here

40
00:01:36.710 --> 00:01:38.060
refer to as init
__ which all here

41
00:01:38.060 --> 00:01:40.580
alright so let's try running this and
refer to as init

42
00:01:40.580 --> 00:01:41.540
see what happens
alright so let's try running this and

43
00:01:41.540 --> 00:01:47.000
alright so the error we're getting here
see what happens

44
00:01:47.000 --> 00:01:49.730
on line 3 is missing one required
alright so the error we're getting here

45
00:01:49.730 --> 00:01:51.350
positional arguments name
on line 3 is missing one required

46
00:01:51.350 --> 00:01:54.110
we've got an error running this code and
positional arguments name

47
00:01:54.110 --> 00:01:55.400
if you think about it the reason is
we've got an error running this code and

48
00:01:55.400 --> 00:01:56.450
quite clear
if you think about it the reason is

49
00:01:56.450 --> 00:01:58.130
that's because we need to pass an
quite clear

50
00:01:58.130 --> 00:02:01.730
argument to the troll constructor when
that's because we need to pass an

51
00:02:01.730 --> 00:02:03.890
we're creating it so i'm going to do is
argument to the troll constructor when

52
00:02:03.890 --> 00:02:06.560
come up here to line 3 and change this
we're creating it so i'm going to do is

53
00:02:06.560 --> 00:02:09.019
so it's got troll and we're going to
come up here to line 3 and change this

54
00:02:09.019 --> 00:02:12.800
put the name in there pug so let's run
so it's got troll and we're going to

55
00:02:12.800 --> 00:02:13.560
that
put the name in there pug so let's run

56
00:02:13.560 --> 00:02:17.099
this time we've actually got an error on
that

57
00:02:17.099 --> 00:02:19.230
line four and we got one below as well
this time we've actually got an error on

58
00:02:19.230 --> 00:02:21.300
which we won't worry about for now but
line four and we got one below as well

59
00:02:21.300 --> 00:02:25.200
the call to print on line we are relying on
which we won't worry about for now but

60
00:02:25.200 --> 00:02:26.880
the string method that we added to the
the call to print on line we are relying on

61
00:02:26.880 --> 00:02:29.310
enemy class that's actually getting an
the string method that we added to the

62
00:02:29.310 --> 00:02:31.319
error here on line 4 and also down
enemy class that's actually getting an

63
00:02:31.319 --> 00:02:34.980
here on line 18 in the enemy class when
error here on line 4 and also down

64
00:02:34.980 --> 00:02:36.030
we tried and that's what we try to
here on line 18 in the enemy class when

65
00:02:36.030 --> 00:02:38.130
access the attributes of our troll
we tried and that's what we try to

66
00:02:38.130 --> 00:02:40.920
instance now by the way when reading
access the attributes of our troll

67
00:02:40.920 --> 00:02:42.540
these stack traces that python
instance now by the way when reading

68
00:02:42.540 --> 00:02:44.550
produces i actually like to read them
these stack traces that python

69
00:02:44.550 --> 00:02:45.600
from the bottom up
produces i actually like to read them

70
00:02:45.600 --> 00:02:47.549
I think they make more sense that way so
from the bottom up

71
00:02:47.549 --> 00:02:49.650
starting at the bottom here our
I think they make more sense that way so

72
00:02:49.650 --> 00:02:51.840
code raise an attribute
starting at the bottom here our

73
00:02:51.840 --> 00:02:54.690
error because our troll object has no
code raise an attribute

74
00:02:54.690 --> 00:02:57.840
attribute name reading upwards the error
error because our troll object has no

75
00:02:57.840 --> 00:03:01.470
happened at line 18 in enemypy
attribute name reading upwards the error

76
00:03:01.470 --> 00:03:03.959
in the string method and that's
happened at line 18 in enemypy

77
00:03:03.959 --> 00:03:05.310
where we were trying to access the
in the string method and that's

78
00:03:05.310 --> 00:03:07.739
attributes to format them into the
where we were trying to access the

79
00:03:07.739 --> 00:03:10.920
string that we want to print and that
attributes to format them into the

80
00:03:10.920 --> 00:03:13.440
was called right here on line 4 in main
string that we want to print and that

81
00:03:13.440 --> 00:03:14.880
which is why we've got this other error
was called right here on line 4 in main

82
00:03:14.880 --> 00:03:16.860
showing that's obviously the
which is why we've got this other error

83
00:03:16.860 --> 00:03:18.870
print statement so what's actually
showing that's obviously the

84
00:03:18.870 --> 00:03:22.170
happened here so why is our troll lost all
print statement so what's actually

85
00:03:22.170 --> 00:03:23.910
the attributes that it just had in the
happened here so why is our troll lost all

86
00:03:23.910 --> 00:03:26.519
previous video well the reason is we
the attributes that it just had in the

87
00:03:26.519 --> 00:03:28.799
added the init method to the troll class
previous video well the reason is we

88
00:03:28.799 --> 00:03:31.350
and when we did that Python longer points the
added the init method to the troll class

89
00:03:31.350 --> 00:03:34.470
enemy classes and init method so it runs the
and when we did that Python longer points the

90
00:03:34.470 --> 00:03:37.440
init method in our troll class instead so
enemy classes and init method so it runs the

91
00:03:37.440 --> 00:03:39.750
if the enemy's init method doesn't run
init method in our troll class instead so

92
00:03:39.750 --> 00:03:42.840
then the attributes don't gets set
if the enemy's init method doesn't run

93
00:03:42.840 --> 00:03:45.239
so what we actually need to do here is
then the attributes don't gets set

94
00:03:45.239 --> 00:03:47.040
call the init method of the superclass
so what we actually need to do here is

95
00:03:47.040 --> 00:03:51.569
enemy inside our trolls init method now
call the init method of the superclass

96
00:03:51.569 --> 00:03:53.220
there's a few ways to do this and i'll
enemy inside our trolls init method now

97
00:03:53.220 --> 00:03:55.829
leave the one I recommend in python 3 to
there's a few ways to do this and i'll

98
00:03:55.829 --> 00:03:58.769
last so we'll go back to our enemy class
leave the one I recommend in python 3 to

99
00:03:58.769 --> 00:04:02.400
and down here to troll now firstly we
last so we'll go back to our enemy class

100
00:04:02.400 --> 00:04:04.590
can actually prefix the call to init
and down here to troll now firstly we

101
00:04:04.590 --> 00:04:07.650
with the name of the superclass so we
can actually prefix the call to init

102
00:04:07.650 --> 00:04:09.180
can do something like get rid of the
with the name of the superclass so we

103
00:04:09.180 --> 00:04:12.420
pass...
can do something like get rid of the

104
00:04:12.420 --> 00:04:15.299
....
pass...

105
00:04:15.299 --> 00:04:15.870
...
....

106
00:04:15.870 --> 00:04:26.370
...
...

107
00:04:26.370 --> 00:04:30.120
but that would still get an error
...

108
00:04:30.120 --> 00:04:32.220
because we've got to these other lines
but that would still get an error

109
00:04:32.220 --> 00:04:35.700
here on lines six and nine got
because we've got to these other lines

110
00:04:35.700 --> 00:04:37.410
multiple parameters we're passing the
here on lines six and nine got

111
00:04:37.410 --> 00:04:39.480
hit points or both the hit points and the
multiple parameters we're passing the

112
00:04:39.480 --> 00:04:42.300
number of lives so let's actually fix
hit points or both the hit points and the

113
00:04:42.300 --> 00:04:44.670
those first so their just the names
number of lives so let's actually fix

114
00:04:44.670 --> 00:04:46.740
they're just one parameter just to see
those first so their just the names

115
00:04:46.740 --> 00:04:52.500
what happens if you run this now the
they're just one parameter just to see

116
00:04:52.500 --> 00:04:54.270
program runs and all our trolls you
what happens if you run this now the

117
00:04:54.270 --> 00:04:56.820
can see now have 23 hitpoints well
program runs and all our trolls you

118
00:04:56.820 --> 00:04:58.050
actually going to say the all do but
can see now have 23 hitpoints well

119
00:04:58.050 --> 00:05:00.480
urgh doesn't that's because we're using the
actually going to say the all do but

120
00:05:00.480 --> 00:05:03.300
enemy class here instead of troll but if I change
urgh doesn't that's because we're using the

121
00:05:03.300 --> 00:05:08.130
that to troll run that again we see now
enemy class here instead of troll but if I change

122
00:05:08.130 --> 00:05:10.980
that they all do have one life and 23 hit points
that to troll run that again we see now

123
00:05:10.980 --> 00:05:13.169
so if they all have different
that they all do have one life and 23 hit points

124
00:05:13.169 --> 00:05:15.540
names so that we can tell them apart
so if they all have different

125
00:05:15.540 --> 00:05:17.669
although telling one troll from another
names so that we can tell them apart

126
00:05:17.669 --> 00:05:19.710
is a specialized skill it won't be
although telling one troll from another

127
00:05:19.710 --> 00:05:21.120
covering that in the course
is a specialized skill it won't be

128
00:05:21.120 --> 00:05:23.040
alright so let's go back to the trolll
covering that in the course

129
00:05:23.040 --> 00:05:26.400
class enemy.py and lets have a look at
alright so let's go back to the trolll

130
00:05:26.400 --> 00:05:29.100
what we did here so we created an init
class enemy.py and lets have a look at

131
00:05:29.100 --> 00:05:31.530
method for our troll class and when we did
what we did here so we created an init

132
00:05:31.530 --> 00:05:33.960
that the init method of enemy is no
method for our troll class and when we did

133
00:05:33.960 --> 00:05:36.419
longer called you could say that the
that the init method of enemy is no

134
00:05:36.419 --> 00:05:38.850
trolls init method had shadowed init
longer called you could say that the

135
00:05:38.850 --> 00:05:41.880
method in its superclass so to get a
trolls init method had shadowed init

136
00:05:41.880 --> 00:05:43.919
around that and make sure that class
method in its superclass so to get a

137
00:05:43.919 --> 00:05:46.740
attributes are initialized we called the
around that and make sure that class

138
00:05:46.740 --> 00:05:49.560
enemy superclass init method that's the
attributes are initialized we called the

139
00:05:49.560 --> 00:05:55.770
call on line 24 by prefixing the method name with the class name now its imporant
enemy superclass init method that's the

140
00:05:55.770 --> 00:05:57.210
that we provide the correct number of
call on line 24 by prefixing the method name with the class name now its imporant

141
00:05:57.210 --> 00:06:00.060
parameters but because the enemy init
that we provide the correct number of

142
00:06:00.060 --> 00:06:02.040
method has default values we could have
parameters but because the enemy init

143
00:06:02.040 --> 00:06:03.510
left off one or more of the parameters
method has default values we could have

144
00:06:03.510 --> 00:06:05.700
out here this ones here
left off one or more of the parameters

145
00:06:05.700 --> 00:06:07.740
you won't always want to provide default
out here this ones here

146
00:06:07.740 --> 00:06:09.690
values in your class methods so it's
you won't always want to provide default

147
00:06:09.690 --> 00:06:11.010
important to remember that we are
values in your class methods so it's

148
00:06:11.010 --> 00:06:12.690
calling the superclass init method
important to remember that we are

149
00:06:12.690 --> 00:06:15.030
here and it needs 4 argument's
calling the superclass init method

150
00:06:15.030 --> 00:06:18.120
now our trolls init method only takes two
here and it needs 4 argument's

151
00:06:18.120 --> 00:06:20.190
arguments so we should provide values
now our trolls init method only takes two

152
00:06:20.190 --> 00:06:22.440
for the remaining two alright so that's
arguments so we should provide values

153
00:06:22.440 --> 00:06:24.120
one way to do it and that would be the
for the remaining two alright so that's

154
00:06:24.120 --> 00:06:27.660
only way available in python 2 now in
one way to do it and that would be the

155
00:06:27.660 --> 00:06:30.270
python three we can use the super
only way available in python 2 now in

156
00:06:30.270 --> 00:06:32.580
method instead and if you want to cope
python three we can use the super

157
00:06:32.580 --> 00:06:34.950
with multiple inheritance you must use
method instead and if you want to cope

158
00:06:34.950 --> 00:06:35.969
super
with multiple inheritance you must use

159
00:06:35.969 --> 00:06:37.469
instead of specifying the base class
super

160
00:06:37.469 --> 00:06:39.989
name so let's do that so i'm going to
instead of specifying the base class

161
00:06:39.989 --> 00:06:42.179
change this enemy part here delete that
name so let's do that so i'm going to

162
00:06:42.179 --> 00:06:45.809
out we're going to put...
change this enemy part here delete that

163
00:06:45.809 --> 00:06:53.309
...
out we're going to put...

164
00:06:53.309 --> 00:06:56.519
...
...

165
00:06:56.519 --> 00:07:00.059
....let's just run that to make sure it
...

166
00:07:00.059 --> 00:07:07.110
still works it still works now syntax
....let's just run that to make sure it

167
00:07:07.110 --> 00:07:09.029
does make it a little bit hard to read
still works it still works now syntax

168
00:07:09.029 --> 00:07:11.579
but what we're basically doing is passing the
does make it a little bit hard to read

169
00:07:11.579 --> 00:07:14.309
name of our class troll and the current
but what we're basically doing is passing the

170
00:07:14.309 --> 00:07:17.339
instance self to super and then we're
name of our class troll and the current

171
00:07:17.339 --> 00:07:19.709
using that to call the init method of
instance self to super and then we're

172
00:07:19.709 --> 00:07:22.019
the base class now when you're using
using that to call the init method of

173
00:07:22.019 --> 00:07:24.299
super inside of class instance there's a
the base class now when you're using

174
00:07:24.299 --> 00:07:26.639
more readable shorthand way of writing
super inside of class instance there's a

175
00:07:26.639 --> 00:07:29.939
unfortunately and we can do away with
more readable shorthand way of writing

176
00:07:29.939 --> 00:07:32.669
this troll and self in the parentheses
unfortunately and we can do away with

177
00:07:32.669 --> 00:07:35.909
just change it so it's got super with
this troll and self in the parentheses

178
00:07:35.909 --> 00:07:37.619
the parentheses dot than the __
just change it so it's got super with

179
00:07:37.619 --> 00:07:40.259
init and that would be the
the parentheses dot than the __

180
00:07:40.259 --> 00:07:42.029
way that I suggest you normally use it
init and that would be the

181
00:07:42.029 --> 00:07:43.919
when calling methods in the superclass
way that I suggest you normally use it

182
00:07:43.919 --> 00:07:46.589
and it does it the identical thing to
when calling methods in the superclass

183
00:07:46.589 --> 00:07:48.209
what we had previously and I will just undo
and it does it the identical thing to

184
00:07:48.209 --> 00:07:54.989
that take a copy of that line and cut
what we had previously and I will just undo

185
00:07:54.989 --> 00:07:56.759
that out
that take a copy of that line and cut

186
00:07:56.759 --> 00:08:00.899
fix it so it's doing the same thing as
that out

187
00:08:00.899 --> 00:08:02.879
the commented out line on line 24
fix it so it's doing the same thing as

188
00:08:02.879 --> 00:08:06.029
but the compiler knows the type troll
the commented out line on line 24

189
00:08:06.029 --> 00:08:08.339
and the instant self so there's really
but the compiler knows the type troll

190
00:08:08.339 --> 00:08:10.229
no need to specify them in the super
and the instant self so there's really

191
00:08:10.229 --> 00:08:10.860
call
no need to specify them in the super

192
00:08:10.860 --> 00:08:14.399
ok so now our trolls behave differently to a
call

193
00:08:14.399 --> 00:08:17.099
basic enemy when we create a new troll
ok so now our trolls behave differently to a

194
00:08:17.099 --> 00:08:19.619
we just give him or her a name and hit
basic enemy when we create a new troll

195
00:08:19.619 --> 00:08:22.169
points are live are automatically set for
we just give him or her a name and hit

196
00:08:22.169 --> 00:08:25.439
us now subclasses can have additional
points are live are automatically set for

197
00:08:25.439 --> 00:08:28.529
attributes to extend their behavior and
us now subclasses can have additional

198
00:08:28.529 --> 00:08:30.299
allow them to do things that their base
attributes to extend their behavior and

199
00:08:30.299 --> 00:08:33.269
class doesn't do so lets demonstrate
allow them to do things that their base

200
00:08:33.269 --> 00:08:36.539
that by giving our trolls a grunt method
class doesn't do so lets demonstrate

201
00:08:36.539 --> 00:08:39.599
will come down here
that by giving our trolls a grunt method

202
00:08:39.599 --> 00:08:45.899
and do...
will come down here

203
00:08:45.899 --> 00:08:52.470
....
and do...

204
00:08:52.470 --> 00:09:02.519
...
....

205
00:09:02.519 --> 00:09:05.730
alright so that's the grunt method added
...

206
00:09:05.730 --> 00:09:07.920
to the troll class so let's get our
alright so that's the grunt method added

207
00:09:07.920 --> 00:09:09.269
trolls to grunt by adding a bit more
to the troll class so let's get our

208
00:09:09.269 --> 00:09:13.019
code in the main py file....
trolls to grunt by adding a bit more

209
00:09:13.019 --> 00:09:16.380
...
code in the main py file....

210
00:09:16.380 --> 00:09:24.180
....
...

211
00:09:24.180 --> 00:09:26.490
...
....

212
00:09:26.490 --> 00:09:33.899
...
...

213
00:09:33.899 --> 00:09:38.579
....
...

214
00:09:38.579 --> 00:09:41.639
....the
....

215
00:09:41.639 --> 00:09:43.170
troubles with trolls is that once you set
....the

216
00:09:43.170 --> 00:09:45.060
one off that you'll have to join in so
troubles with trolls is that once you set

217
00:09:45.060 --> 00:09:46.439
let's go ahead and actually add the code
one off that you'll have to join in so

218
00:09:46.439 --> 00:09:49.500
for the others so we'll do another troll....
let's go ahead and actually add the code

219
00:09:49.500 --> 00:09:53.220
....
for the others so we'll do another troll....

220
00:09:53.220 --> 00:10:00.029
....and then run that me
....

221
00:10:00.029 --> 00:10:02.339
pug pug stop stomping me ugh ughs
....and then run that me

222
00:10:02.339 --> 00:10:05.519
stomp you stomp you then me urg urgh
pug pug stop stomping me ugh ughs

223
00:10:05.519 --> 00:10:08.100
so about now a wise adventure might be
stomp you stomp you then me urg urgh

224
00:10:08.100 --> 00:10:10.470
decided that it's time to leave so
so about now a wise adventure might be

225
00:10:10.470 --> 00:10:13.139
getting back to our troll sub class
decided that it's time to leave so

226
00:10:13.139 --> 00:10:15.389
it can now do things that a basic
getting back to our troll sub class

227
00:10:15.389 --> 00:10:17.490
enemy cant and if we try and get an
it can now do things that a basic

228
00:10:17.490 --> 00:10:19.410
enemy instance to grant them then will get an
enemy cant and if we try and get an

229
00:10:19.410 --> 00:10:21.389
error so just to demonstrate that
enemy instance to grant them then will get an

230
00:10:21.389 --> 00:10:28.649
....
error so just to demonstrate that

231
00:10:28.649 --> 00:10:33.329
...
....

232
00:10:33.329 --> 00:10:36.509
...
...

233
00:10:36.509 --> 00:10:40.380
...and if you try to run that not
...

234
00:10:40.380 --> 00:10:42.930
surprising we get an error enemy object
...and if you try to run that not

235
00:10:42.930 --> 00:10:46.290
has no attribute grunt we just highlight
surprising we get an error enemy object

236
00:10:46.290 --> 00:10:47.670
that with the mouse unresolved
has no attribute grunt we just highlight

237
00:10:47.670 --> 00:10:49.559
attribute reference grunt for class enemy
that with the mouse unresolved

238
00:10:49.559 --> 00:10:52.170
which again isn't surprising because it
attribute reference grunt for class enemy

239
00:10:52.170 --> 00:10:52.660
hasn't
which again isn't surprising because it

240
00:10:52.660 --> 00:10:54.730
the enemy class hasn't got a grunt
hasn't

241
00:10:54.730 --> 00:10:55.779
method
the enemy class hasn't got a grunt

242
00:10:55.779 --> 00:10:57.790
ok so as well as adding extra behavior
method

243
00:10:57.790 --> 00:11:00.490
to our subclasses we can now also change
ok so as well as adding extra behavior

244
00:11:00.490 --> 00:11:03.009
the behavior of methods that exists in
to our subclasses we can now also change

245
00:11:03.009 --> 00:11:05.920
the superclass to see how to do that
the behavior of methods that exists in

246
00:11:05.920 --> 00:11:08.079
we're going to start off by creating a
the superclass to see how to do that

247
00:11:08.079 --> 00:11:10.660
new class but let's start working on
we're going to start off by creating a

248
00:11:10.660 --> 00:11:17.279
that in the next video
new class but let's start working on