WEBVTT

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in the last video we saw how subclasses

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can take advantage of all the attributes
in the last video we saw how subclasses

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data attributes and methods of their
can take advantage of all the attributes

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superclass and we also added extra
data attributes and methods of their

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functionality to our subclasses to give
superclass and we also added extra

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them extra attributes that their base
functionality to our subclasses to give

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class didn't have in this video we're
them extra attributes that their base

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going to see how to change the behavior
class didn't have in this video we're

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further so that a subclass can implement
going to see how to change the behavior

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a method from its superclass and
further so that a subclass can implement

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actually do things differently now vampire
a method from its superclass and

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are shifty creatures they don't get to
actually do things differently now vampire

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live for all eternity without learning a
are shifty creatures they don't get to

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few tricks after all so what we're going
live for all eternity without learning a

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to do is change the take damage method
few tricks after all so what we're going

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so that vampires can dodge when attacked
to do is change the take damage method

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can turn into a bat or move super fast
so that vampires can dodge when attacked

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or whatever trick they learnt
can turn into a bat or move super fast

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to avoid getting bashed so going to
or whatever trick they learnt

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choose a random element so that our
to avoid getting bashed so going to

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vampire has a one-in-three chance of
choose a random element so that our

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dodging a blow
vampire has a one-in-three chance of

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now we've used the random module before
dodging a blow

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and we're going to use it again here to
now we've used the random module before

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generate a random number between one on
and we're going to use it again here to

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the three inclusive and if we get a
generate a random number between one on

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three vampires successfully dodges the blow
the three inclusive and if we get a

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let's open up the vampire class which is
three vampires successfully dodges the blow

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if you recall is in our enemy.py
let's open up the vampire class which is

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script we're going to come down here and
if you recall is in our enemy.py

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start to make some changes so we're
script we're going to come down here and

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going to do is start and create the
start to make some changes so we're

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dodges method so....
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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...so we now
...

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got a method which is quite simple
...so we now

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and if the number generated is three
got a method which is quite simple

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we're going to print a message that the
and if the number generated is three

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vampire Dodges and return true
we're going to print a message that the

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otherwise it returns false now one
vampire Dodges and return true

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thing you might be wondering is looking
otherwise it returns false now one

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at code is why i imported the random
thing you might be wondering is looking

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method on line 43 into this method rather
at code is why i imported the random

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than putting it at the top of the module
method on line 43 into this method rather

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and to be honest I'm actually wondering
than putting it at the top of the module

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that myself and seriously though what i
and to be honest I'm actually wondering

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have done is show you that it can be
that myself and seriously though what i

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done there so you may see it in code
have done is show you that it can be

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that you have to maintain and in rare
done there so you may see it in code

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cases it may even make sense to do it
that you have to maintain and in rare

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like this
cases it may even make sense to do it

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now with that said that most of the time
like this

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I suggest you don't do it like this i'm
now with that said that most of the time

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going to take my own advice and remove the
I suggest you don't do it like this i'm

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import to the start of the module we're
going to take my own advice and remove the

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it belongs ok write at to the top there
import to the start of the module we're

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ok so we now defined the Dodges
it belongs ok write at to the top there

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method for the vampire added an extra
ok so we now defined the Dodges

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few lines their just for clarity with
method for the vampire added an extra

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subtitles but i'll remove that too at
few lines their just for clarity with

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some point
subtitles but i'll remove that too at

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alright so that's better at this point
some point

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we now no longer import the random module
alright so that's better at this point

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every time the Dodge method is called and
we now no longer import the random module

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if we need to use random numbers in
every time the Dodge method is called and

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another enemy class object it's now
if we need to use random numbers in

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available to all the adventure games are
another enemy class object it's now

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traditionally played with dice so we
available to all the adventure games are

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will most certainly want to include
traditionally played with dice so we

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random behavior elsewhere and even if we knew
will most certainly want to include

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we only ever use the random module
random behavior elsewhere and even if we knew

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the Dodge method it's still not a good
we only ever use the random module

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idea to perform the import their
the Dodge method it's still not a good

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alright so now we're going to change the
idea to perform the import their

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behavior of our vampires when their
alright so now we're going to change the

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attacked but before we do that let's
behavior of our vampires when their

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swing back over to the main python script
attacked but before we do that let's

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and test our dodged method so
swing back over to the main python script

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we're going to put some code down here
and test our dodged method so

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so before line 28
we're going to put some code down here

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we're going to put....
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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so lets just run this to see that it does work
...

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we can see if we scroll up that vlads
so lets just run this to see that it does work

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doggers I think it should fix that
we can see if we scroll up that vlads

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dodges that is better try that
doggers I think it should fix that

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again and we should see now that vlad our
dodges that is better try that

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vampires should randomly dodge
again and we should see now that vlad our

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dodge there and it's a
vampires should randomly dodge

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one-in-three chance just run it one more time
dodge there and it's a

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theirs another dodge so we can say
one-in-three chance just run it one more time

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that we are getting different results it is
theirs another dodge so we can say

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random and we can see that vlad our
that we are getting different results it is

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vampire is dodging some of the attacks
random and we can see that vlad our

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so it does seem to be working we saw
vampire is dodging some of the attacks

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that the last time I run it there
so it does seem to be working we saw

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the Dodges came up less i think there's
that the last time I run it there

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any actually one dodge there for the
the Dodges came up less i think there's

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whole run and you will find situations
any actually one dodge there for the

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because it's random where that vlad
whole run and you will find situations

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won't dodge at all and it's also possible
because it's random where that vlad

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for him to dodge every blow and never die
won't dodge at all and it's also possible

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but it's actually not very likely
for him to dodge every blow and never die

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alright so we've added a new method to
but it's actually not very likely

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the vampire class to give them the
alright so we've added a new method to

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ability to dodge what we really want is
the vampire class to give them the

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for that behavior to be built into the
ability to dodge what we really want is

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class rather than our main program
for that behavior to be built into the

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having to check that during each attack
class rather than our main program

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so to do that we're going to override
having to check that during each attack

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the take
so to do that we're going to override

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_damage method that the vampire
the take

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class inherits from enemy now don't
_damage method that the vampire

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confuse overriding a method with
class inherits from enemy now don't

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overloading it as i mentioned earlier
confuse overriding a method with

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overloading doesn't exist in python so
overloading it as i mentioned earlier

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if you're not sure what it is then don't
overloading doesn't exist in python so

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worry because you can't actually do it
if you're not sure what it is then don't

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anyway but overriding a method that
worry because you can't actually do it

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means replacing it with another one now
anyway but overriding a method that

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in languages such as Java and C++ there
means replacing it with another one now

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are restrictions on the definition of an
in languages such as Java and C++ there

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overriding method in Python you just write
are restrictions on the definition of an

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a new method with the same name as the
overriding method in Python you just write

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one that you want to override the new
a new method with the same name as the

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method doesn't even have to have the
one that you want to override the new

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same or accept the same number of
method doesn't even have to have the

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parameters although it usually will so
same or accept the same number of

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lets override the enemy
parameters although it usually will so

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classes take damage method to make
lets override the enemy

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it do something different in the vampire
classes take damage method to make

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class going to come up and work on our
it do something different in the vampire

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vampire class and what we're going to do
class going to come up and work on our

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is come down here and add another
vampire class and what we're going to do

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method we're going to type...
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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...let's just run it like I have
...

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defined it on line 52 and see what
...let's just run it like I have

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happens when I run it and see we
defined it on line 52 and see what

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can get
happens when I run it and see we

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or we are getting into an infinite loop so
can get

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i want to stop the program so let's
or we are getting into an infinite loop so

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actually go back and look at what
i want to stop the program so let's

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happened now in our main py script we
actually go back and look at what

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keep on looping as long as the vamp is
happened now in our main py script we

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alive on line 27 that method the method
keep on looping as long as the vamp is

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that can result in an enemy no longer
alive on line 27 that method the method

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being alive is the take_damage
that can result in an enemy no longer

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method in the enemy class so when our
being alive is the take_damage

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vampire object use that method which
method in the enemy class so when our

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they inherit from enemy the program
vampire object use that method which

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works but now that we've given the
they inherit from enemy the program

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vampire class its own take_
works but now that we've given the

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damage method that's the method being
vampire class its own take_

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called up here on line 29 the new method
damage method that's the method being

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that we defined for the vampire now
called up here on line 29 the new method

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because the vampire version of the
that we defined for the vampire now

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method doesn't do anything yet
because the vampire version of the

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therefore our vampire never dies now
method doesn't do anything yet

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that may be a feature of vampires but
therefore our vampire never dies now

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it's going to make for a very boring
that may be a feature of vampires but

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game but it does show now that we
it's going to make for a very boring

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are calling the vampire class take_damage
game but it does show now that we

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method rather than the enemy
are calling the vampire class take_damage

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one it really does confirm that that method
method rather than the enemy

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is being executed and not the original
one it really does confirm that that method

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take_damage method from the
is being executed and not the original

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superclass which in this case
take_damage method from the

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was the enemy class that's why i ran it
superclass which in this case

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at this stage just to make that clear
was the enemy class that's why i ran it

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but what we want to do here is call the super
at this stage just to make that clear

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version of take damage but change things
but what we want to do here is call the super

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slightly so that our vampires can still
version of take damage but change things

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dodge now we've already seen how to call
slightly so that our vampires can still

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a super method from a subclass when we
dodge now we've already seen how to call

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created the init method for the troll
a super method from a subclass when we

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and vampire classes so now we can do the
created the init method for the troll

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same thing for take_damage
and vampire classes so now we can do the

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we only want to take damage if the
same thing for take_damage

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vampire doesn't dodge so let's write the
we only want to take damage if the

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code for that so going back to our enemy
vampire doesn't dodge so let's write the

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class to our vampire class whether i'm
code for that so going back to our enemy

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going to get rid of this pass instead what
class to our vampire class whether i'm

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we're going to put in here is....
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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...so we are using super just like we did
...

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when we call these superclasses init
...so we are using super just like we did

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method you can see that on line 43 only
when we call these superclasses init

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this time we are calling the take_
method you can see that on line 43 only

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damage method now by calling take_
this time we are calling the take_

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damage like this we don't to write all
damage method now by calling take_

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the code again we just wrap the call
damage like this we don't to write all

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to the super method in a test to see
the code again we just wrap the call

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whether the vampire dodges or should
to the super method in a test to see

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take damage the other advantage is now
whether the vampire dodges or should

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we don't need to put the testing in our
take damage the other advantage is now

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main program let's put that back so we
we don't need to put the testing in our

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can take out this if not vamped
main program let's put that back so we

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Dodges now back to what it was and i
can take out this if not vamped

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just comment that out of print for now
Dodges now back to what it was and i

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if we run this we should see that it
just comment that out of print for now

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works vlad is down eventually
if we run this we should see that it

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and his got heaps dodging you can see these
works vlad is down eventually

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are quire a few Dodges this time this
and his got heaps dodging you can see these

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particular occasion is taking damage as
are quire a few Dodges this time this

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well and then he is dead and he's now dead on
particular occasion is taking damage as

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the last line and again because of the
well and then he is dead and he's now dead on

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random element the number of Dodges each
the last line and again because of the

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time will vary greatly but over time it
random element the number of Dodges each

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should be roughly one-third of each
time will vary greatly but over time it

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attack that results in a successful
should be roughly one-third of each

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dodge now note that vlad sometimes starts off
attack that results in a successful

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with all 12 hit points because you
dodge now note that vlad sometimes starts off

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sometimes dodge the attack when we
with all 12 hit points because you

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attempt to take five points of damage
sometimes dodge the attack when we

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here on line 20 so in other words the
attempt to take five points of damage

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ability to dodge is now part of the
here on line 20 so in other words the

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vampire subclass and although
ability to dodge is now part of the

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vampires inherit from enemy they
vampire subclass and although

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now behave differently when attacked
vampires inherit from enemy they

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so you've now seen two of the really
now behave differently when attacked

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important benefits of using inheritance
so you've now seen two of the really

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when creating classes first our sub
important benefits of using inheritance

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classes get all the attributes that's
when creating classes first our sub

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the data and methods that are defined in
classes get all the attributes that's

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their base class also known as a
the data and methods that are defined in

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superclass so that we don't have to
their base class also known as a

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write the same code again and again for
superclass so that we don't have to

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each sub class
write the same code again and again for

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but second we can also extend or alter
each sub class

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the behavior of a class by creating a
but second we can also extend or alter

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subclass that adds extra methods or
the behavior of a class by creating a

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changes the behavior of an existing
subclass that adds extra methods or

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method we're going to see an example of
changes the behavior of an existing

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that in the next section when we
method we're going to see an example of

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subclass the TK inter ist box so that
that in the next section when we

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it populates itself with data from a
subclass the TK inter ist box so that

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database now there's one other thing we
it populates itself with data from a

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00:11:09.709 --> 00:11:11.720
might want to do with our classes and
database now there's one other thing we

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00:11:11.720 --> 00:11:13.730
in fact if we were going to do this then
might want to do with our classes and

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we should have done from the start
in fact if we were going to do this then

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however i left the two now because if
we should have done from the start

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you do then you might have a problem
however i left the two now because if

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with IntelliJ is renaming of variables
you do then you might have a problem

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00:11:21.380 --> 00:11:23.839
so to see what the potential problem is
with IntelliJ is renaming of variables

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00:11:23.839 --> 00:11:27.110
we look at the code here what i'm going to do
so to see what the potential problem is

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is I'm just going to comment out these
we look at the code here what i'm going to do

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first two lines and i'm going to put
is I'm just going to comment out these

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00:11:35.089 --> 00:11:37.670
another line of code in here....
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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....you can see here that I've
...

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added some code that modified vlad lives
....you can see here that I've

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and hit points attributes directly if
added some code that modified vlad lives

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00:11:54.740 --> 00:11:59.630
you run this and surprisingly vlads ends
and hit points attributes directly if

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up with no lives left and hit points
you run this and surprisingly vlads ends

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set to only one that's normal behavior
up with no lives left and hit points

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for python and as we've seen a few times
set to only one that's normal behavior

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we can't prevent code from accessing the
for python and as we've seen a few times

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data attributes of our classes what we
we can't prevent code from accessing the

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can do is providing indication
data attributes of our classes what we

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that this shouldn't be done and if you
can do is providing indication

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remember the convention is to prefix the
that this shouldn't be done and if you

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attribute names with an underscore now
remember the convention is to prefix the

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ideally we would have done this right from
attribute names with an underscore now

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the start and in fact of i'd recommend
ideally we would have done this right from

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prefixing your class data attributes with
the start and in fact of i'd recommend

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an underscore right away if you decide you
prefixing your class data attributes with

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00:12:31.790 --> 00:12:33.800
want that to you want to hide them and
an underscore right away if you decide you

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if you do find that you need to access
want that to you want to hide them and

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00:12:35.390 --> 00:12:37.910
them directly you can refactor the ones
if you do find that you need to access

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that do require direct access or at a
them directly you can refactor the ones

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00:12:40.070 --> 00:12:41.810
property for them as we saw in a
that do require direct access or at a

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00:12:41.810 --> 00:12:43.250
previous video in this section of the
property for them as we saw in a

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course so the decision on whether to
previous video in this section of the

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00:12:46.070 --> 00:12:48.800
hide the attributes or not isn't
course so the decision on whether to

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00:12:48.800 --> 00:12:50.779
necessarily a simple one and there
hide the attributes or not isn't

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really are no hard and fast rules that
necessarily a simple one and there

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apply to all scenarios
really are no hard and fast rules that

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now keep in mind that the python
apply to all scenarios

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philosophy is that you probably
now keep in mind that the python

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shouldn't hide them
philosophy is that you probably

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unless modifying them directly will break your
shouldn't hide them

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00:13:02.210 --> 00:13:05.060
code somehow so modifying the lives
unless modifying them directly will break your

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00:13:05.060 --> 00:13:06.470
and hit points as we're doing here
code somehow so modifying the lives

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on line 31 and 32 won't break the code
and hit points as we're doing here

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00:13:10.430 --> 00:13:13.790
so i'd be tempted to leave them as they
on line 31 and 32 won't break the code

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00:13:13.790 --> 00:13:15.860
were but as I want to show you a
so i'd be tempted to leave them as they

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00:13:15.860 --> 00:13:17.750
potential pitfall with renaming
were but as I want to show you a

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00:13:17.750 --> 00:13:19.940
attributes in IntelliJ we'll go ahead
potential pitfall with renaming

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00:13:19.940 --> 00:13:21.920
and mark them as private for one of a
attributes in IntelliJ we'll go ahead

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00:13:21.920 --> 00:13:24.230
better term when I use the term private
and mark them as private for one of a

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00:13:24.230 --> 00:13:25.670
in Python remember i'm talking about
better term when I use the term private

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00:13:25.670 --> 00:13:28.820
intention and things aren't really private
in Python remember i'm talking about

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00:13:28.820 --> 00:13:30.110
alright so we can just go ahead and
intention and things aren't really private

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00:13:30.110 --> 00:13:32.030
refactor our attributes in the enemy
alright so we can just go ahead and

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00:13:32.030 --> 00:13:36.170
class go back to enemy going up here
refactor our attributes in the enemy

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00:13:36.170 --> 00:13:37.370
because it's the enemy class that we
class go back to enemy going up here

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00:13:37.370 --> 00:13:39.350
wanted do our reflecting on going to
because it's the enemy class that we

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00:13:39.350 --> 00:13:41.660
start here with a self.name so
wanted do our reflecting on going to

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00:13:41.660 --> 00:13:44.090
going to right click on name refactor
start here with a self.name so

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00:13:44.090 --> 00:13:48.050
rename just going to add an underscore
going to right click on name refactor

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00:13:48.050 --> 00:13:51.980
to the name press enter so changes
rename just going to add an underscore

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00:13:51.980 --> 00:13:55.250
reflected and going to the same for
to the name press enter so changes

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00:13:55.250 --> 00:13:57.830
hitpoints lives and the life
reflected and going to the same for

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00:13:57.830 --> 00:14:01.010
so each one i'm just going to rename just
hitpoints lives and the life

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00:14:01.010 --> 00:14:09.830
putting _ at the start
so each one i'm just going to rename just

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alright so that's all 4 now you can
putting _ at the start

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00:14:18.290 --> 00:14:20.750
see here as an example self dot
alright so that's all 4 now you can

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00:14:20.750 --> 00:14:22.940
underscore hit_points equals
see here as an example self dot

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00:14:22.940 --> 00:14:24.890
remaining points as an example of what
underscore hit_points equals

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00:14:24.890 --> 00:14:26.420
intelliJ has done when it's refactored
remaining points as an example of what

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00:14:26.420 --> 00:14:28.790
and renamed things for us so switching
intelliJ has done when it's refactored

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00:14:28.790 --> 00:14:31.910
back to main we can see here that the
and renamed things for us so switching

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00:14:31.910 --> 00:14:33.770
attributes have been renamed as well so
back to main we can see here that the

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00:14:33.770 --> 00:14:35.270
intelliJ done that when we use
attributes have been renamed as well so

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00:14:35.270 --> 00:14:40.880
the refactor but eventually run this we
intelliJ done that when we use

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00:14:40.880 --> 00:14:43.610
actually get an error troll object has
the refactor but eventually run this we

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00:14:43.610 --> 00:14:47.090
no attribute name so intelliJ
actually get an error troll object has

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00:14:47.090 --> 00:14:49.250
normally does a great job but it does
no attribute name so intelliJ

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00:14:49.250 --> 00:14:51.080
fall down on those replacement fields
normally does a great job but it does

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00:14:51.080 --> 00:14:53.330
that we've used before in the enemy
fall down on those replacement fields

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00:14:53.330 --> 00:14:54.410
class in our underscore underscore
that we've used before in the enemy

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00:14:54.410 --> 00:14:59.150
string method this method here and
class in our underscore underscore

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00:14:59.150 --> 00:15:01.070
going back to the error
string method this method here and

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00:15:01.070 --> 00:15:02.450
luckily it's actually telling us its
going back to the error

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00:15:02.450 --> 00:15:04.940
line 27 in the underscore underscore
luckily it's actually telling us its

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00:15:04.940 --> 00:15:07.130
string underscore underscore method so
line 27 in the underscore underscore

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00:15:07.130 --> 00:15:08.900
we have a look at that again that is
string underscore underscore method so

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00:15:08.900 --> 00:15:10.790
this line here so you can see what the
we have a look at that again that is

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00:15:10.790 --> 00:15:12.530
problem is that intelliJ hasn't
this line here so you can see what the

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00:15:12.530 --> 00:15:14.390
actually rename those replacement fields
problem is that intelliJ hasn't

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00:15:14.390 --> 00:15:16.820
correctly now we could just edit up those
actually rename those replacement fields

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00:15:16.820 --> 00:15:19.370
occurrences manually but we've also got
correctly now we could just edit up those

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00:15:19.370 --> 00:15:21.620
to change lines in some other places as
occurrences manually but we've also got

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00:15:21.620 --> 00:15:23.720
well like for example on line 21 and
to change lines in some other places as

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00:15:23.720 --> 00:15:26.330
line 23 they are both referring to the old
well like for example on line 21 and

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00:15:26.330 --> 00:15:27.860
name before it was prefixed with an _
line 23 they are both referring to the old

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00:15:27.860 --> 00:15:29.780
so it's really a bit of work to
name before it was prefixed with an _

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00:15:29.780 --> 00:15:32.000
do here and going down looking at the
so it's really a bit of work to

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00:15:32.000 --> 00:15:33.680
troll we've actually got will
do here and going down looking at the

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00:15:33.680 --> 00:15:35.030
need to do some working there as well the
troll we've actually got will

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00:15:35.030 --> 00:15:37.280
troll grunt method hasn't an _
need to do some working there as well the

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00:15:37.280 --> 00:15:39.980
for the data attributes anymore either
troll grunt method hasn't an _

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00:15:39.980 --> 00:15:41.660
so quite a bit of work to actually go
for the data attributes anymore either

356
00:15:41.660 --> 00:15:43.490
right through and refactor this if we
so quite a bit of work to actually go

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00:15:43.490 --> 00:15:45.740
wanted to do it so it's quite a lot of
right through and refactor this if we

358
00:15:45.740 --> 00:15:48.110
work and as I mentioning to do this and
wanted to do it so it's quite a lot of

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00:15:48.110 --> 00:15:50.000
I want to draw your attention to a
work and as I mentioning to do this and

360
00:15:50.000 --> 00:15:52.700
possible pitfall with refactoring data
I want to draw your attention to a

361
00:15:52.700 --> 00:15:54.770
attributes but i'm going to show you a
possible pitfall with refactoring data

362
00:15:54.770 --> 00:15:57.740
quick way to do with that next important
attributes but i'm going to show you a

363
00:15:57.740 --> 00:15:59.330
thing here is that you can get problems
quick way to do with that next important

364
00:15:59.330 --> 00:16:00.710
if you use this form of replacement
thing here is that you can get problems

365
00:16:00.710 --> 00:16:03.170
fields and then try to refactor the
if you use this form of replacement

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00:16:03.170 --> 00:16:05.360
attributes later alright so i'm going to
fields and then try to refactor the

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00:16:05.360 --> 00:16:07.310
end the video here now in the next video
attributes later alright so i'm going to

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00:16:07.310 --> 00:16:08.270
will continue on and we're actually
end the video here now in the next video

369
00:16:08.270 --> 00:16:10.310
going to bring some regular expressions
will continue on and we're actually

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00:16:10.310 --> 00:16:12.710
to try and fix this issue so see you in
going to bring some regular expressions

371
00:16:12.710 --> 00:16:18.280
the next video
to try and fix this issue so see you in