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so at the end of the last video we

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created troll class which if you recall

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was a subclass of enemy at the moment

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it's not doing anything useful as you

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saw we could just as easily use an enemy

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instead and get exactly the same result

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so inspired by his brothers fine example

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ugs game or has been going to the gym and

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working out in fact he's still a bit of

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a trend and now all the trolls have

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been toughened up so every trolls that

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our adventurers encounter in this game

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will now take 23 points of damage now

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because they're mortal only have one

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life so there's no need to specify

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either value when we create them what we

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need to do is initialize the troll

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instances with just a name so that we

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can tell them apart the hit points and

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lives will be the same for every troll

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that we create so going back to our

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enemy class where our trolls are defined

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at the moment we just got pass in their so

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we're going to change that we're going

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to actually delete that and then we're

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going to come down here we're going to

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add our init....

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....

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....

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...

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...

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so the hit points and lives will be the same

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for every troll we create the name the

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instance rather is just going to have a

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name and that's why we're passing it as

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a parameter to the constructor to the

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init method the underscore underscore init

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init method the underscore underscore init

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00:01:38,460 --> 00:01:40,410
__ which all here

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refer to as init

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alright so let's try running this and

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see what happens

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alright so the error we're getting here

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on line 3 is missing one required

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positional arguments name

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we've got an error running this code and

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if you think about it the reason is

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quite clear

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that's because we need to pass an

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argument to the troll constructor when

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we're creating it so i'm going to do is

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come up here to line 3 and change this

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so it's got troll and we're going to

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put the name in there pug so let's run

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that

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this time we've actually got an error on

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line four and we got one below as well

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which we won't worry about for now but

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the call to print on line we are relying on

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the string method that we added to the

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enemy class that's actually getting an

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error here on line 4 and also down

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here on line 18 in the enemy class when

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we tried and that's what we try to

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access the attributes of our troll

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instance now by the way when reading

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these stack traces that python

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produces i actually like to read them

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from the bottom up

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I think they make more sense that way so

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starting at the bottom here our

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code raise an attribute

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error because our troll object has no

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attribute name reading upwards the error

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happened at line 18 in enemypy

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in the string method and that's

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where we were trying to access the

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attributes to format them into the

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string that we want to print and that

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was called right here on line 4 in main

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which is why we've got this other error

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showing that's obviously the

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print statement so what's actually

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happened here so why is our troll lost all

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the attributes that it just had in the

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previous video well the reason is we

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added the init method to the troll class

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and when we did that Python longer points the

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enemy classes and init method so it runs the

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init method in our troll class instead so

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if the enemy's init method doesn't run

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then the attributes don't gets set

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so what we actually need to do here is

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call the init method of the superclass

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enemy inside our trolls init method now

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there's a few ways to do this and i'll

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leave the one I recommend in python 3 to

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last so we'll go back to our enemy class

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00:04:02,460 --> 00:04:06,100
and down here to troll now firstly we

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can actually prefix the call to init

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with the name of the superclass so we

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can do something like get rid of the

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pass...

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....

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...

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...

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but that would still get an error
...

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because we've got to these other lines

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here on lines six and nine got

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multiple parameters we're passing the

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hit points or both the hit points and the

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number of lives so let's actually fix

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those first so their just the names

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they're just one parameter just to see

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what happens if you run this now the

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program runs and all our trolls you

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can see now have 23 hitpoints well

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actually going to say the all do but

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urgh doesn't that's because we're using the

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enemy class here instead of troll but if I change

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that to troll run that again we see now

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that they all do have one life and 23 hit points

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so if they all have different

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names so that we can tell them apart

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although telling one troll from another

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is a specialized skill it won't be

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covering that in the course

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alright so let's go back to the trolll

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class enemy.py and lets have a look at

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what we did here so we created an init

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method for our troll class and when we did

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that the init method of enemy is no

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longer called you could say that the

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trolls init method had shadowed init

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method in its superclass so to get a

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around that and make sure that class

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attributes are initialized we called the

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enemy superclass init method that's the

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call on line 24 by prefixing the method name with the class name now its imporant

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that we provide the correct number of

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parameters but because the enemy init

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method has default values we could have

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left off one or more of the parameters

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out here this ones here

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you won't always want to provide default

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values in your class methods so it's

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important to remember that we are

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calling the superclass init method

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here and it needs 4 argument's

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now our trolls init method only takes two

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arguments so we should provide values

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for the remaining two alright so that's

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one way to do it and that would be the

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only way available in python 2 now in

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python three we can use the super

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method instead and if you want to cope

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with multiple inheritance you must use

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super

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instead of specifying the base class

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name so let's do that so i'm going to

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change this enemy part here delete that

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out we're going to put...

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...

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...

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....let's just run that to make sure it

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still works it still works now syntax

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does make it a little bit hard to read

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but what we're basically doing is passing the

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name of our class troll and the current

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instance self to super and then we're

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using that to call the init method of

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the base class now when you're using

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super inside of class instance there's a

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more readable shorthand way of writing

175
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unfortunately and we can do away with

176
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this troll and self in the parentheses

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just change it so it's got super with

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the parentheses dot than the __

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init and that would be the

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way that I suggest you normally use it

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when calling methods in the superclass

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and it does it the identical thing to

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what we had previously and I will just undo

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that take a copy of that line and cut

185
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that out

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fix it so it's doing the same thing as

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the commented out line on line 24

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but the compiler knows the type troll

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and the instant self so there's really

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00:08:12,030 --> 00:08:13,920
no need to specify them in the super

191
00:08:13,920 --> 00:08:14,560
call

192
00:08:14,560 --> 00:08:18,090
ok so now our trolls behave differently to a

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00:08:18,090 --> 00:08:20,790
basic enemy when we create a new troll

194
00:08:20,790 --> 00:08:23,310
we just give him or her a name and hit

195
00:08:23,310 --> 00:08:25,860
points are live are automatically set for

196
00:08:25,860 --> 00:08:29,130
us now subclasses can have additional

197
00:08:29,130 --> 00:08:32,220
attributes to extend their behavior and

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00:08:32,220 --> 00:08:33,990
allow them to do things that their base

199
00:08:33,990 --> 00:08:36,960
class doesn't do so lets demonstrate

200
00:08:36,960 --> 00:08:40,230
that by giving our trolls a grunt method

201
00:08:40,230 --> 00:08:43,289
will come down here

202
00:08:43,289 --> 00:08:49,590
and do...

203
00:08:49,590 --> 00:08:56,170
....

204
00:08:56,170 --> 00:09:06,210
...

205
00:09:06,210 --> 00:09:09,430
alright so that's the grunt method added

206
00:09:09,430 --> 00:09:11,620
to the troll class so let's get our

207
00:09:11,620 --> 00:09:12,960
trolls to grunt by adding a bit more

208
00:09:12,960 --> 00:09:16,710
code in the main py file....

209
00:09:16,710 --> 00:09:20,080
...

210
00:09:20,080 --> 00:09:27,880
....

211
00:09:27,880 --> 00:09:30,190
...

212
00:09:30,190 --> 00:09:37,590
...

213
00:09:37,590 --> 00:09:42,270
....

214
00:09:42,270 --> 00:09:45,330
....the

215
00:09:45,330 --> 00:09:46,870
troubles with trolls is that once you set

216
00:09:46,870 --> 00:09:48,760
one off that you'll have to join in so

217
00:09:48,760 --> 00:09:50,130
let's go ahead and actually add the code

218
00:09:50,130 --> 00:09:53,200
for the others so we'll do another troll....

219
00:09:53,200 --> 00:09:56,920
....

220
00:09:56,920 --> 00:10:03,720
....and then run that me

221
00:10:03,720 --> 00:10:06,030
pug pug stop stomping me ugh ughs

222
00:10:06,030 --> 00:10:09,210
stomp you stomp you then me urg urgh

223
00:10:09,210 --> 00:10:11,800
so about now a wise adventure might be

224
00:10:11,800 --> 00:10:14,170
decided that it's time to leave so

225
00:10:14,170 --> 00:10:16,830
getting back to our troll sub class

226
00:10:16,830 --> 00:10:19,080
it can now do things that a basic

227
00:10:19,080 --> 00:10:21,190
enemy cant and if we try and get an

228
00:10:21,190 --> 00:10:23,110
enemy instance to grant them then will get an

229
00:10:23,110 --> 00:10:25,080
error so just to demonstrate that

230
00:10:25,080 --> 00:10:32,340
....

231
00:10:32,340 --> 00:10:37,020
...

232
00:10:37,020 --> 00:10:40,200
...

233
00:10:40,200 --> 00:10:44,080
...and if you try to run that not

234
00:10:44,080 --> 00:10:46,630
surprising we get an error enemy object

235
00:10:46,630 --> 00:10:49,990
has no attribute grunt we just highlight

236
00:10:49,990 --> 00:10:51,370
that with the mouse unresolved

237
00:10:51,370 --> 00:10:53,250
attribute reference grunt for class enemy

238
00:10:53,250 --> 00:10:55,870
which again isn't surprising because it

239
00:10:55,870 --> 00:10:56,360
hasn't

240
00:10:56,360 --> 00:10:58,430
the enemy class hasn't got a grunt

241
00:10:58,430 --> 00:10:59,470
method

242
00:10:59,470 --> 00:11:01,490
ok so as well as adding extra behavior

243
00:11:01,490 --> 00:11:04,190
to our subclasses we can now also change

244
00:11:04,190 --> 00:11:06,700
the behavior of methods that exists in

245
00:11:06,700 --> 00:11:09,620
the superclass to see how to do that

246
00:11:09,620 --> 00:11:11,770
we're going to start off by creating a

247
00:11:11,770 --> 00:11:14,360
new class but let's start working on

248
00:11:14,360 --> 00:11:20,970
that in the next video