1
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so once again with now got a working
program but it is now time to remove

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those circular references that we've
talked about previously now there is no

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need for the song class to store an
artist object anymore we now have a way

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to find an artist in the list if we know the
artist's name and that's using the find_

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00:00:24,590 --> 00:00:30,410
object function which you've seen as using the
code and in addition theirs no need for the

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album class to store the artist object
once again the name is all that we need

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to be able to

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00:00:35,740 --> 00:00:40,360
reference that again using the find_object function so it makes

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things a lot easier and the class diagram
is now much simplified and I just want to bring

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that up on screen you can see there that we can
simply this a lot with it is

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simplified by removing that

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relationship so once we do that we'll
end up with something like this

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the top diagram as you can see there so
that's what we're trying to achieve so

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how do we go about doing that and removing the
circular references

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00:01:06,710 --> 00:01:11,380
well thats the challenge this is the challenge that I'm gonna set you to actually fix in this

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video so let me just paste in the text for the challenge so you know what is exactly needs to be done ok so here is what we

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want to do we want to modify the program so
that the class structure matches the

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simplified diagram now artist objects can
hold references to album objects and album

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objects can hold references to song
objects but the key here is there must

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be no circular references so that is really
what you're trying to achieve here is to

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remove that or set up so their aren't circular references so its now time to do that

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so pause the video and go away and see if you can complete that challenge when you

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ready to come back and check our
solution start the video again and I'll

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go through and show you how to do that

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ok so hopefully you managed to solve it so let's go
through and see if we can get this working

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so I'm just going to undo these
changes and removed this from the doc

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strings because we don't need it their so what need to do well the first change is in the song class and what we gonna do is first change

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the doc string to reflect the fact that
the song subject is now going to store the

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name of the artists rather
than a reference to the artist object so

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00:02:22,840 --> 00:02:27,370
come up to the class song which is on
the screen at the moment

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we got artist which is an artist we are going to change
it because it is going to be a string now and it's

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going to be the name of the songs
creator....

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00:02:40,620 --> 00:02:45,650
and we don't need to make any other
changes its pretty straightforward

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00:02:45,650 --> 00:02:49,900
that's really all we need to do with the
song class but of course when we create

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new song objects were gonna be passing
the artists name as a string to the init

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00:02:53,100 --> 00:02:57,080
method instead of passing the artist
object and we are doing this to remove

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circular references so the next step is
to go ahead and do that to remove the

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00:03:01,390 --> 00:03:04,660
circular reference between album and
artist

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00:03:04,660 --> 00:03:09,970
so go to class album and bring it on the screen
here so artists the artists responsible

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00:03:09,970 --> 00:03:11,610
for the album if not specified

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00:03:11,610 --> 00:03:20,830
this is now going to be a string here
that's the name of the artist name of the

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00:03:20,830 --> 00:03:24,010
artist as supposed to the object responsible for the
album and if not specified

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00:03:24,580 --> 00:03:27,980
that's all exactly the same as it what it was before

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00:03:27,980 --> 00:03:35,290
down here on line 39 we got self.artist equals various artist if the parameter

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00:03:35,290 --> 00:03:38,270
pass or the argument pass was none we are going to
change that

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00:03:38,270 --> 00:03:42,500
so you no longer going to be trying to create an artist object we are going to be setting that to string

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00:03:42,500 --> 00:03:47,540
the string of various artists that's
all the change we need here now the

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00:03:47,540 --> 00:03:51,970
add song method doesn't need to be changed
the reason for that is that it uses

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00:03:51,970 --> 00:03:56,720
self.artist and then now we are storing
artist as a string that will automatically

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00:03:56,720 --> 00:04:02,200
be used when creating the songs so finally
we need to change the artists class so

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00:04:02,200 --> 00:04:06,730
that when it creates a new album it's using
its name rather than passing self

52
00:04:06,730 --> 00:04:10,930
so in that way the artist class will only be
storing the artist name as a string rather

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00:04:10,930 --> 00:04:15,180
than storing a reference to the artist
object as it is currently doing so

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00:04:15,180 --> 00:04:17,620
scrolling down to look at the artist class

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00:04:17,620 --> 00:04:22,710
the change will make the album we

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00:04:22,710 --> 00:04:26,010
got equals new album name year and self

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00:04:26,010 --> 00:04:32,880
we no longer want to pass self we want to pass
the attribute self.name so that is

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00:04:32,880 --> 00:04:36,750
literally the only things that we should
need to change at this point the program

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00:04:36,750 --> 00:04:41,660
should know run and will tests that shortly
so the artists class stores references

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00:04:41,660 --> 00:04:46,110
to albums in its list now and the album
class towards references to songs but

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they aren't circular references any longer
so neither the song class nor the album

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class store artist objects anymore they
just hold the name of the artist as a

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string and of course they get looked up with
the find_object function when we

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00:04:58,420 --> 00:05:02,590
need to find out more information about
that so lets run this and confirm that

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00:05:02,590 --> 00:05:13,820
it does run...so we will run this and we still get the same
results as we got before so everything is

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00:05:13,820 --> 00:05:17,660
working nicely with the changes that
we're actually made so that's actually it

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that is a basic introduction to
object-oriented programming in Python and

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00:05:22,420 --> 00:05:28,070
we've seen what classes are now and how to create our own basic classes and

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00:05:28,070 --> 00:05:33,110
we also look at the concepts of encapsulation and delegation now by taking a program and

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00:05:33,110 --> 00:05:37,660
changing it to use object oriented
techniques hopefully we've given you an

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appreciation of how this alternative
approach can really provide huge benefit

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and reliability and also allow you to become
more productive at the same time now we

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have really only scratched the surface
of object oriented programming is really

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a lot more to cover yet and in Python their is also different implementation options to

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consider so I'm going to be covering all that in
the remaining videos in the section so

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I'll see you in the next one