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in the last video we saw how subclasses

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can take advantage of all the attributes

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data attributes and methods of their

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superclass and we also added extra

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functionality to our subclasses to give

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them extra attributes that their base

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class didn't have in this video we're

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going to see how to change the behavior

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further so that a subclass can implement

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a method from its superclass and

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actually do things differently now vampire

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are shifty creatures they don't get to

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live for all eternity without learning a

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few tricks after all so what we're going

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to do is change the take damage method

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so that vampires can dodge when attacked

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can turn into a bat or move super fast

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or whatever trick they learnt

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to avoid getting bashed so going to

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choose a random element so that our

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vampire has a one-in-three chance of

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dodging a blow

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now we've used the random module before

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and we're going to use it again here to

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generate a random number between one on

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the three inclusive and if we get a

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three vampires successfully dodges the blow

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let's open up the vampire class which is

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if you recall is in our enemy.py

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script we're going to come down here and

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start to make some changes so we're

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going to do is start and create the

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dodges method so....

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....

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....

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...

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...

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...so we now

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got a method which is quite simple

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and if the number generated is three

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we're going to print a message that the

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vampire Dodges and return true

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otherwise it returns false now one

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thing you might be wondering is looking

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at code is why i imported the random

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method on line 43 into this method rather

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than putting it at the top of the module

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and to be honest I'm actually wondering

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that myself and seriously though what i

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have done is show you that it can be

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done there so you may see it in code

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that you have to maintain and in rare

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cases it may even make sense to do it

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like this

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now with that said that most of the time

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I suggest you don't do it like this i'm

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going to take my own advice and remove the

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import to the start of the module we're

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it belongs ok write at to the top there

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ok so we now defined the Dodges

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method for the vampire added an extra

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few lines their just for clarity with

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subtitles but i'll remove that too at

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some point

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alright so that's better at this point

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we now no longer import the random module

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every time the Dodge method is called and

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if we need to use random numbers in

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another enemy class object it's now

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available to all the adventure games are

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traditionally played with dice so we

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will most certainly want to include

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random behavior elsewhere and even if we knew

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we only ever use the random module

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the Dodge method it's still not a good

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idea to perform the import their

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alright so now we're going to change the

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behavior of our vampires when their

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attacked but before we do that let's

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swing back over to the main python script

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and test our dodged method so

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we're going to put some code down here

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so before line 28

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we're going to put....

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....

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....

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...

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so lets just run this to see that it does work

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we can see if we scroll up that vlads

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doggers I think it should fix that

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dodges that is better try that

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again and we should see now that vlad our

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vampires should randomly dodge

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dodge there and it's a

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one-in-three chance just run it one more time

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theirs another dodge so we can say

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that we are getting different results it is

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random and we can see that vlad our

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vampire is dodging some of the attacks

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so it does seem to be working we saw

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that the last time I run it there

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the Dodges came up less i think there's

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any actually one dodge there for the

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whole run and you will find situations

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because it's random where that vlad

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won't dodge at all and it's also possible

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for him to dodge every blow and never die

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but it's actually not very likely

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alright so we've added a new method to

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the vampire class to give them the

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ability to dodge what we really want is

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for that behavior to be built into the

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class rather than our main program

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having to check that during each attack

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so to do that we're going to override

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the take

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_damage method that the vampire

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class inherits from enemy now don't

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confuse overriding a method with

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overloading it as i mentioned earlier

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overloading doesn't exist in python so

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if you're not sure what it is then don't

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worry because you can't actually do it

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anyway but overriding a method that

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means replacing it with another one now

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in languages such as Java and C++ there

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are restrictions on the definition of an

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overriding method in Python you just write

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a new method with the same name as the

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one that you want to override the new

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method doesn't even have to have the

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same or accept the same number of

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parameters although it usually will so

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lets override the enemy

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classes take damage method to make

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it do something different in the vampire

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class going to come up and work on our

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vampire class and what we're going to do

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is come down here and add another

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method we're going to type...

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...

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...

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....

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...

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...

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...let's just run it like I have

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defined it on line 52 and see what

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happens when I run it and see we

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can get

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or we are getting into an infinite loop so

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i want to stop the program so let's

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actually go back and look at what

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happened now in our main py script we

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keep on looping as long as the vamp is

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alive on line 27 that method the method

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that can result in an enemy no longer

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being alive is the take_damage

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method in the enemy class so when our

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vampire object use that method which

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they inherit from enemy the program

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works but now that we've given the

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vampire class its own take_

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damage method that's the method being

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called up here on line 29 the new method

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that we defined for the vampire now

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because the vampire version of the

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method doesn't do anything yet

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therefore our vampire never dies now

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that may be a feature of vampires but

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it's going to make for a very boring

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game but it does show now that we

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are calling the vampire class take_damage

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method rather than the enemy

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one it really does confirm that that method

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is being executed and not the original

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take_damage method from the

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superclass which in this case

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was the enemy class that's why i ran it

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at this stage just to make that clear

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but what we want to do here is call the super

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version of take damage but change things

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slightly so that our vampires can still

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dodge now we've already seen how to call

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a super method from a subclass when we

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created the init method for the troll

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and vampire classes so now we can do the

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same thing for take_damage

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we only want to take damage if the

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vampire doesn't dodge so let's write the

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code for that so going back to our enemy

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class to our vampire class whether i'm

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going to get rid of this pass instead what

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we're going to put in here is....

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....

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...

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...so we are using super just like we did

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when we call these superclasses init

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method you can see that on line 43 only

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this time we are calling the take_

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damage method now by calling take_

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damage like this we don't to write all

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the code again we just wrap the call

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to the super method in a test to see

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whether the vampire dodges or should

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take damage the other advantage is now

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we don't need to put the testing in our

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main program let's put that back so we

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can take out this if not vamped

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Dodges now back to what it was and i

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just comment that out of print for now

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if we run this we should see that it

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works vlad is down eventually

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and his got heaps dodging you can see these

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are quire a few Dodges this time this

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particular occasion is taking damage as

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well and then he is dead and he's now dead on

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the last line and again because of the

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random element the number of Dodges each

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time will vary greatly but over time it

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should be roughly one-third of each

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attack that results in a successful

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dodge now note that vlad sometimes starts off

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with all 12 hit points because you

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sometimes dodge the attack when we

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attempt to take five points of damage

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here on line 20 so in other words the

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ability to dodge is now part of the

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vampire subclass and although

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vampires inherit from enemy they

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now behave differently when attacked

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so you've now seen two of the really

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important benefits of using inheritance

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when creating classes first our sub

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classes get all the attributes that's

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the data and methods that are defined in

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their base class also known as a

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superclass so that we don't have to

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write the same code again and again for

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each sub class

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but second we can also extend or alter

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the behavior of a class by creating a

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subclass that adds extra methods or

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changes the behavior of an existing

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method we're going to see an example of

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that in the next section when we

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subclass the TK inter ist box so that

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it populates itself with data from a

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database now there's one other thing we

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might want to do with our classes and

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in fact if we were going to do this then

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we should have done from the start

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however i left the two now because if

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you do then you might have a problem

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with IntelliJ is renaming of variables

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so to see what the potential problem is

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we look at the code here what i'm going to do

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is I'm just going to comment out these

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first two lines and i'm going to put

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another line of code in here....

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...

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...

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....you can see here that I've

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added some code that modified vlad lives

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and hit points attributes directly if

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you run this and surprisingly vlads ends

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up with no lives left and hit points

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set to only one that's normal behavior

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for python and as we've seen a few times

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we can't prevent code from accessing the

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data attributes of our classes what we

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can do is providing indication

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that this shouldn't be done and if you

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remember the convention is to prefix the

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attribute names with an underscore now

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ideally we would have done this right from

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the start and in fact of i'd recommend

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prefixing your class data attributes with

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an underscore right away if you decide you

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want that to you want to hide them and

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if you do find that you need to access

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them directly you can refactor the ones

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that do require direct access or at a

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property for them as we saw in a

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previous video in this section of the

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course so the decision on whether to

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hide the attributes or not isn't

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necessarily a simple one and there

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really are no hard and fast rules that

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apply to all scenarios

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now keep in mind that the python

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philosophy is that you probably

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shouldn't hide them

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unless modifying them directly will break your

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code somehow so modifying the lives

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and hit points as we're doing here

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on line 31 and 32 won't break the code

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so i'd be tempted to leave them as they

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were but as I want to show you a

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potential pitfall with renaming

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attributes in IntelliJ we'll go ahead

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and mark them as private for one of a

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better term when I use the term private

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in Python remember i'm talking about

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intention and things aren't really private

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alright so we can just go ahead and

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refactor our attributes in the enemy

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class go back to enemy going up here

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because it's the enemy class that we

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wanted do our reflecting on going to

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start here with a self.name so

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going to right click on name refactor

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rename just going to add an underscore

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to the name press enter so changes

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reflected and going to the same for

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hitpoints lives and the life

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so each one i'm just going to rename just

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putting _ at the start

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alright so that's all 4 now you can

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see here as an example self dot

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underscore hit_points equals

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remaining points as an example of what

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intelliJ has done when it's refactored

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and renamed things for us so switching

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back to main we can see here that the

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attributes have been renamed as well so

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intelliJ done that when we use

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the refactor but eventually run this we

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actually get an error troll object has

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no attribute name so intelliJ

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normally does a great job but it does

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fall down on those replacement fields

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that we've used before in the enemy

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class in our underscore underscore

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string method this method here and

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going back to the error

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luckily it's actually telling us its

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line 27 in the underscore underscore

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string underscore underscore method so

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we have a look at that again that is

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this line here so you can see what the

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problem is that intelliJ hasn't

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actually rename those replacement fields

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correctly now we could just edit up those

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occurrences manually but we've also got

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to change lines in some other places as

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well like for example on line 21 and

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line 23 they are both referring to the old

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name before it was prefixed with an _

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so it's really a bit of work to

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do here and going down looking at the

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troll we've actually got will

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need to do some working there as well the

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troll grunt method hasn't an _

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for the data attributes anymore either

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so quite a bit of work to actually go

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right through and refactor this if we

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wanted to do it so it's quite a lot of

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work and as I mentioning to do this and

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I want to draw your attention to a

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possible pitfall with refactoring data

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attributes but i'm going to show you a

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quick way to do with that next important

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thing here is that you can get problems

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if you use this form of replacement

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fields and then try to refactor the

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attributes later alright so i'm going to

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end the video here now in the next video

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will continue on and we're actually

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going to bring some regular expressions

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to try and fix this issue so see you in

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the next video