WEBVTT

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so as promised in the previous video now

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time for a mini-challenge but just a
so as promised in the previous video now

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point before we start don't spend more
time for a mini-challenge but just a

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than a minute or two thinking about this
point before we start don't spend more

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one
than a minute or two thinking about this

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it is designed to be just something you
one

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should hopefully just get off the top of
it is designed to be just something you

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your head so don't spend again too much
should hopefully just get off the top of

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time on it
your head so don't spend again too much

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so the challenge here is looking at the
time on it

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way the last two examples have been
so the challenge here is looking at the

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coded generally what is the difference
way the last two examples have been

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between the approach taken here in all
coded generally what is the difference

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the previous example we use prior
between the approach taken here in all

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to that in this course have a think
the previous example we use prior

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about that and come back when you
to that in this course have a think

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ready end i will give you some more
about that and come back when you

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information about that
ready end i will give you some more

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okay welcome back the answer simply is
information about that

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there's no real difference at all so the
okay welcome back the answer simply is

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two of these two examples use classes
there's no real difference at all so the

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but apart from the fact that i wrote the
two of these two examples use classes

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classes in the program's is no real
but apart from the fact that i wrote the

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difference to the methodology that
classes in the program's is no real

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we employed in other words if the song
difference to the methodology that

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album and artist classes had been part
we employed in other words if the song

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of the standard library then there's
album and artist classes had been part

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nothing to distinguish the approach here from
of the standard library then there's

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anything else that we've done so far
nothing to distinguish the approach here from

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so this program uses objects but it's
anything else that we've done so far

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not object orientated programming
so this program uses objects but it's

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object-oriented program is not just
not object orientated programming

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about classes it's a different way of
object-oriented program is not just

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thinking about problems and results in a
about classes it's a different way of

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different program design so it uses
thinking about problems and results in a

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classes and objects for sure but it also
different program design so it uses

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includes important concepts such as
classes and objects for sure but it also

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encapsulation composition inheritance
includes important concepts such as

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and delegation now I have discuss
encapsulation composition inheritance

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encapsulation at the start of this
and delegation now I have discuss

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section we're going to be looking at
encapsulation at the start of this

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inheritance and composition in later
section we're going to be looking at

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videos delegation on the other hand
inheritance and composition in later

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involves passing on responsibility for a
videos delegation on the other hand

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task to another object that's better
involves passing on responsibility for a

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suited to deal with it and it's fairly
task to another object that's better

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you know real really closely tied to
suited to deal with it and it's fairly

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encapsulation now for example we've
you know real really closely tied to

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been encapsulated data in our classes but
encapsulation now for example we've

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we haven't really encapsulated methods
been encapsulated data in our classes but

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very well now there's an add song
we haven't really encapsulated methods

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method in the album class and an add
very well now there's an add song

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album method in the artist class but you
method in the album class and an add

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know that's really it
album method in the artist class but you

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these two methods were included because
know that's really it

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the relevant classes own the lists that they will be
these two methods were included because

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added to so it seemed quite natural
the relevant classes own the lists that they will be

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that the artist class should be
added to so it seemed quite natural

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responsible for adding album object to
that the artist class should be

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the list but this only considers the
responsible for adding album object to

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data has been no attempt to encapsulate
the list but this only considers the

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the functionality of the program
data has been no attempt to encapsulate

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encapsulation involves encapsulating
the functionality of the program

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data and methods
encapsulation involves encapsulating

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it's not just data so we really need
data and methods

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to make some changes to turn this into
it's not just data so we really need

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an object-oriented program rather than
to make some changes to turn this into

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just a program that happens to use
an object-oriented program rather than

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objects then there's obviously an
just a program that happens to use

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important distinction between those two
objects then there's obviously an

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encapsulating methods means considering
important distinction between those two

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questions such as which object is best
encapsulating methods means considering

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suited to dealing with this task or
questions such as which object is best

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where the responsibility for a performing
suited to dealing with this task or

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this function belong so relating this to
where the responsibility for a performing

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the real world if my car breaks down i'm
this function belong so relating this to

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going to look for someone who can
the real world if my car breaks down i'm

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encapsulates the knowledge of how to
going to look for someone who can

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fix it
encapsulates the knowledge of how to

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mechanic in this case so my local
fix it

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mechanic has been programmed by
mechanic in this case so my local

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attending college perhaps with a knowledge
mechanic has been programmed by

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necessary to fix a car so i'm going to
attending college perhaps with a knowledge

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delegate the job to him or her
necessary to fix a car so i'm going to

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similarly if I want an extension on my
delegate the job to him or her

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house i'm not going to try building
similarly if I want an extension on my

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myself going to find someone who's got
house i'm not going to try building

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the skills to do this for me so and that's
myself going to find someone who's got

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of course unless you're builder a
the skills to do this for me so and that's

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builder encapsulates the skills required
of course unless you're builder a

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to build something that won't fall down or
builder encapsulates the skills required

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leak in the rain and consequently I
to build something that won't fall down or

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delegate that task to them so relating
leak in the rain and consequently I

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this back to our program looking at our
delegate that task to them so relating

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load data method bring that up on the
this back to our program looking at our

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screen that function is doing all the
load data method bring that up on the

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work of parsing the data and working out
screen that function is doing all the

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what to do when it finds a new album and
work of parsing the data and working out

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a new song really though the object that
what to do when it finds a new album and

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knows the most about albums is the
a new song really though the object that

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artists and albums know all about songs
knows the most about albums is the

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so we really should encapsulate the
artists and albums know all about songs

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methods for dealing with albums in the
so we really should encapsulate the

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artist class and for dealing with songs in
methods for dealing with albums in the

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the album class so once that's done load
artist class and for dealing with songs in

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data can delegate dealing with is to the
the album class so once that's done load

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appropriate class will start by
data can delegate dealing with is to the

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rewriting the load data function to
appropriate class will start by

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delegate most of the work to the artists
rewriting the load data function to

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class now when doing this I'm going to
delegate most of the work to the artists

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be calling methods that haven't yet
class now when doing this I'm going to

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been written now this may seem an odd
be calling methods that haven't yet

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thing to do but an object-oriented
been written now this may seem an odd

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approach means you don't have to worry
thing to do but an object-oriented

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about how something is done you focus on
approach means you don't have to worry

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the fact that you needed to be done and
about how something is done you focus on

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something else will be responsible for
the fact that you needed to be done and

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getting it done so that would make more
something else will be responsible for

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sense when you see the load data code so
getting it done so that would make more

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let's go ahead and do that
sense when you see the load data code so

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so the first thing we want to do now if
let's go ahead and do that

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load data is we're going to delete this
so the first thing we want to do now if

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first bit of initialization code we no
load data is we're going to delete this

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longer need that so delete those three
first bit of initialization code we no

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lines they're or to be precise just
longer need that so delete those three

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just those first two we want to leave
lines they're or to be precise just

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the artist_list we still need
just those first two we want to leave

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that
the artist_list we still need

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...what I'm going to do
that

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is that even though it's going to
...what I'm going to do

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involve some code that has already been
is that even though it's going to

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that exists on screen I'm going to delete it
involve some code that has already been

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and retype some of this in just so you can
that exists on screen I'm going to delete it

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see sort of much easier what's been
and retype some of this in just so you can

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changed so i'm going to leave the width code
see sort of much easier what's been

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so we were obviously
changed so i'm going to leave the width code

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initializing the list on line 92
so we were obviously

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this basic code here that retrieves the
initializing the list on line 92

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dialogue from albums . txt that's not
this basic code here that retrieves the

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going to change and we still going to
dialogue from albums . txt that's not

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leave that printing out but after
going to change and we still going to

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that i'm going to remove all that code
leave that printing out but after

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and delete it because we can
that i'm going to remove all that code

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substantially reduce the amount of code
and delete it because we can

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here so I'm now on line 101 and we're
substantially reduce the amount of code

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going to process each entry that we're
here so I'm now on line 101 and we're

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receiving or getting from the albums.txt
going to process each entry that we're

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so...
receiving or getting from the albums.txt

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...
so...

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...so we're looking for the
...

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artist based on the name attribute which we
...so we're looking for the

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talk about extensively in the last video
artist based on the name attribute which we

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and if the new artist is set to none
talk about extensively in the last video

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meaning that we weren't able to find it
and if the new artist is set to none

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in the list already then we're going to
meaning that we weren't able to find it

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create new artist....
in the list already then we're going to

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...
create new artist....

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...
...

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...and that's that's it
...

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so the first part of the function is
...and that's that's it

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unchanged the artist class isn't
so the first part of the function is

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interested in the fact that data is
unchanged the artist class isn't

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coming from a text file
interested in the fact that data is

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nor is interested in the fact that it's
coming from a text file

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red as a tab-delimited list and so load
nor is interested in the fact that it's

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data as a result continues to be responsible
red as a tab-delimited list and so load

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for reading the data and splitting it
data as a result continues to be responsible

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into the correct fields and of course
for reading the data and splitting it

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that's the code from line
into the correct fields and of course

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94 to 98 the list of artists belongs
that's the code from line

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to the main programs so load data also
94 to 98 the list of artists belongs

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retains responsibility for creating a
to the main programs so load data also

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new artist object after checking that
retains responsibility for creating a

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one doesn't already exist with the
new artist object after checking that

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code here on line 102
one doesn't already exist with the

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that's all it does so everything else
code here on line 102

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you can see now is delegated to the
that's all it does so everything else

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artist class by calling ist add song
you can see now is delegated to the

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method on line 106 and then providing
artist class by calling ist add song

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it with the fields remaining fields the
method on line 106 and then providing

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album field the year field in the song
it with the fields remaining fields the

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field so that it can go ahead and create
album field the year field in the song

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that at this point we're not interested
field so that it can go ahead and create

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in how the add song method does
that at this point we're not interested

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we'll work i know that the song will
in how the add song method does

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need to be added somehow but the focus
we'll work i know that the song will

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here is on dealing with artists only a
need to be added somehow but the focus

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little worried about how add song will
here is on dealing with artists only a

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function when I get around to coding it
little worried about how add song will

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until then I'm just gonna call it and
function when I get around to coding it

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not worry about it so it might seem
until then I'm just gonna call it and

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strange calling a method that doesn't
not worry about it so it might seem

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exist and you know of course the
strange calling a method that doesn't

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program won't work until it does exist but
exist and you know of course the

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if you think about it it's really no
program won't work until it does exist but

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different from delegating the repair of
if you think about it it's really no

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a car to a mechanic you know in other
different from delegating the repair of

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words I don't need any idea what the
a car to a mechanic you know in other

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mechanic will do it don't need to be a
words I don't need any idea what the

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mechanic and I don't need to understand how to fix
mechanic will do it don't need to be a

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a car I just know that the car needs
mechanic and I don't need to understand how to fix

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fixing
a car I just know that the car needs

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so I can call my mechanic and say fix
fixing

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the car and I do say hello first and please
so I can call my mechanic and say fix

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afterwards of course but basically it
the car and I do say hello first and please

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boils down to it I'm calling my
afterwards of course but basically it

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mechanics fix_car method and
boils down to it I'm calling my

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hopefully i'm pretty confident that when
mechanics fix_car method and

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the car returns it will be fixed so I'm
hopefully i'm pretty confident that when

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sure you agree that looking at this code
the car returns it will be fixed so I'm

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now it's fast simple then my previous
sure you agree that looking at this code

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version as a result much easy to
now it's fast simple then my previous

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understand and in fact creating a
version as a result much easy to

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flowchart this would probably be totally
understand and in fact creating a

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over-the-top because the code that we've
flowchart this would probably be totally

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got now in our load data
over-the-top because the code that we've

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function pretty much document
got now in our load data

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itself so now that the main program has
function pretty much document

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been written it's time to focus on the
itself so now that the main program has

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details of that adds song method that were
been written it's time to focus on the

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calling on line 106 so what
details of that adds song method that were

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we'll do is we'll create that method
calling on line 106 so what

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first and then explain what it's doing
we'll do is we'll create that method

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let's go back up to the artist class
first and then explain what it's doing

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that we have defined the code for that
let's go back up to the artist class

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we're going to add this method now
that we have defined the code for that

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this add song after the add album
we're going to add this method now

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method so add here...
this add song after the add album

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...
method so add here...

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...
...

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ok so that's our doc string for this
...

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method so let's start by writing it i'm
ok so that's our doc string for this

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just gonna move this up a little bit so
method so let's start by writing it i'm

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you can see more of the screen so we're
just gonna move this up a little bit so

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gonna start I will actually type
you can see more of the screen so we're

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it out then we'll talk about a little
gonna start I will actually type

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bit more so...
it out then we'll talk about a little

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...
bit more so...

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...
...

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ok so hopefully the doc string that i
...

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added on line 82 really says all that
ok so hopefully the doc string that i

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needs to be said so add_song uses
added on line 82 really says all that

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the name of the album to check if an album
needs to be said so add_song uses

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is already present in the list of
the name of the album to check if an album

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albums and then create a new album if it
is already present in the list of

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isn't or if it doesn't exist in other
albums and then create a new album if it

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words it's not present the list of
isn't or if it doesn't exist in other

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albums anything else that needs to be
words it's not present the list of

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done is been delegated to the album's
albums anything else that needs to be

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to the album class add song method
done is been delegated to the album's

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the artist class knows about albums so
to the album class add song method

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it deals with the album part it doesn't
the artist class knows about albums so

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know about songs that's left to the
it deals with the album part it doesn't

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album class to deal with
know about songs that's left to the

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once again I don't care what the album
album class to deal with

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classes add song method does at this
once again I don't care what the album

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stage I just know i'm going to call it
classes add song method does at this

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and let the album class handle what
stage I just know i'm going to call it

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happens and you saw me add print
and let the album class handle what

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statements here so that we can see
happens and you saw me add print

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what's happening when we come to run the
statements here so that we can see

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program but the rest of the code again
what's happening when we come to run the

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once again pretty much document itself
program but the rest of the code again

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so i'm going to finish the video here
once again pretty much document itself

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now I don't know why I added a semi colon at
so i'm going to finish the video here

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the end by the way wrong programming language
now I don't know why I added a semi colon at

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so I'm going to finish the video here in the
the end by the way wrong programming language

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next video we'll come back and will
so I'm going to finish the video here in the

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implement the album class add song method
next video we'll come back and will

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so that we can delegate the task of
implement the album class add song method

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dealing with the song to that method so
so that we can delegate the task of

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see you in the next video
dealing with the song to that method so