WEBVTT

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so it's now time to focus on the album
classes add song method that we've

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delegated the task of dealing with the
song too you can see that currently when the

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artist class we wanna go to the album
class in the file that is obviously this

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one starting on line16 so obviously it already
exists but we need to make some changes to

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get this to work so we are gonna change the
arguments a little bit different it's

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going to be the title..

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and we need to make some changes here at the moment
we've got some very basic validation

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here so we need to use the find object
function in this code to find the

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song if it even exists the track so put...

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...so we are looking for the song tracks if it exists in

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the list and if...

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...so we are creating the new object for the song then

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below that we gonna put.....

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....

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...so the else is going to be....

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....

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.....so what we doing here well the methods have now change to accept a string for

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the song title rather than a sing
object after all the method is called by

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the artists class which doesn't know
about songs and the body of the method is

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similar to what it was but this is just
that extra step that I added to check if

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the songs are already present and then to create a new
song object if it isn't and if the song was

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already present and no action is taken

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now this may or may not be the correct
thing to do

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bonus tracks on CD is often have the
same name as the track in the main album

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and in this case it will result in the
bonus track not being added so to deal

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with this we probably include the track
number and the data file and check that

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rather than or possibly as well as
the title so that's pretty much it the

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method uses the same find_object function to check the list and

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find_object relies on items in
the list some searching for an

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attribute called name which you have seen a
few times now in the previous videos so

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if you run the program now we will probably get an error

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and I'll just run it show you and we do get an error

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song object has no attribute name and
there's a reason for that again find_object relies on

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items in the list that its searching
having an attribute called name and in this

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case the songs title is stored in an attribute called title rather than name but

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that turns out to be pretty easy to fix
we can just change the self.title to

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self.name so come here to line 11 self.title equals title again

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initialization for song and will make that self.name instead of title....

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so we are now using names as an attribute for title and we also want to change the create_

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check file function so right down
here

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on line 141 so at the moment that's got title their we want to change the title to be

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name as well so of course thats printing out the title attribute from

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song object but we're now
changing that to use the name attribute because we renamed

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the attribute

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and we will just delete the checkfile.txt....and lets run this again

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and we can see its now processing as we expected to do and we can see theirs 28 artist

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now because the program hasn't been
released and nobody's relying on the

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song class in the code changing the
attribute in this way that we've done in

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this video is fine but if we hadn't
released the program and their was a chance

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that other people could be importing it
you know to use our classes in changing

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attribute wouldn't be a good idea and
would have to

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take another approach instead but I'll
come back to an alternative approach to

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that in a minute but the program is now
taking an object oriented approach and

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as a result it's a lot
easier to understand it's also easy to

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modify if necessary and theirs less chance of bugs creeping in when we do so simpler code is

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generally more reliable and by
delegating tasks to other objects we've

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kept each step much simpler and more
focused on a single task rather than

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having that huge load_data method that we did previously so hopefully seeing how this

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program is changed

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was trying change to use object oriented
techniques help to demonstrate some of

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the advantages that object oriented
programming can provide now it's not

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essential to use object oriented
techniques and sometimes an extra

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overhead that goes with it can impact
performance and a functional imperative

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approach might be more suitable but when
used correctly though object oriented

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programming can result in simpler code fewer errors and ultimately

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faster development now before I finish with this example for now anyway

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we are gonna removed the secular references from our
objects and also make this program work

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without renaming the song classes
title attribute or at least show

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a way to allow code that used title to still work even though our code expects the

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attribute to be called name so first we
need to do is go back close this window

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down go back to line 11 again and
we're gonna change the self.name back

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to title so we can see that
alternative approach back to title again

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and obviously the program will crash and we go down and change checkfile

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again as well change this back to title as
well

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and by doing that the program is back in
the state where it wouldn't work because

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the find object functions expecting its
objects to have a name field or

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an attribute which if won't have of course because we just
changed name back to title now because

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we want to run the program after
removing the circular references we have

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to fix the problem with the title attribute first so that
it can compile at least so I'm gonna explain this

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next step in more detail on a later video but
for now I just want to show that this is

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possible now also anyone who's
experienced in object-oriented

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programming might be concerned that our
classes are allowing direct access to

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the attributes now this isn't
necessarily a bad thing

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remembering that Python does things
differently but this is also good

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opportunity to show you that you can
allow access via getters and setters and

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you can even restrict access so that
getters and setters are the only way to retrieve

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and change attributes so to do that we need
to go back up to our song class and

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come down here we need to introduce a
new method and put...

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....

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...

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....

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so as I mentioned the get_title method is a getter for those people who are

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used to object oriented programming and
if this is your first experience of

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object oriented programming then don't
worry if you don't know what a getter

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is because I'm going to be explaining all that
later but below that on line 18 I

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defined a read only property called
name that uses the getter to return the

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value of the title attribute so in this way
existing code such as the create_check

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file function will still work but
we've then be able to use the find

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object function as well so if we run this bearing in mind that last time we run this with the self.title

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changes in here

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the original code it crashed because It
couldn't find the name attribute

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but now we've added this on line 18 and I'll add another line to keep IntelliJ happy if we run this now we see that

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the code now does work nicely even
though there isn't technically a name

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attribute in our song class so what we've done is
we've added a property called name to

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the song class to allow it to be used
without find_object function

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and we've done so without breaking any existing code so you can see that that's another alternative

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that would be very important if your
code had been released and being used by

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other people and as I said I'm going to be covering getters and setters in this method of defining

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properties in later video and when I do
that you'll also see why I didn't just set

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self.name = title in the init method
so in other words I didn't do something

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like this..so when I do show
you that in a video I'm gonna demonstrate why

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I didn't do that do that approach and why I used property instead so remove that for now so

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we are back to the fact that we've got
a working program so the next video we

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going to go through remove the circular
references and then we'll move on to a

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challenge so see in the next video