WEBVTT

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- [Instructor] So in the last
few videos, we've produced

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a scrollable subclass of
the tkinter Listbox class.

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We then populated the list
from our music database.

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So we've got everything we
need to move the database

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functionality into another
subclass to produce a listbox

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that automatically displays
data from a database table.

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But before we start, we
have to decide how we're

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going to initialise the
instances of our new class.

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Now, we're obviously
going to have to tell it

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the name of the table that it should get

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the data from and which
field it needs to display.

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So it's a good idea to provide
a database connexion as well

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so that our classes don't have
to rely on a global variable.

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A sort order would also be useful.

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The songs should be listed in track order,

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the order they appear on the album,

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but we're displaying the song titles.

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So sorting by the song title wouldn't be

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what users were expecting to see.

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Now, we can make the default
sort order the displayed field

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so that if a different
sort order isn't specified,

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the list will then sort
the items alphabetically.

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Now, at the moment, when
we run the programme,

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only one of our listboxes
displays data to start with.

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So what we need is some way to trigger

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the initial load of
data for those instances

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that will display data as
soon as they're created.

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And we also need some way

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to get the other listboxes
to load their data

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once we know the ID of
the artist or album,

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and in fact it would make
sense to use the same method

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in both cases and just
pass none for the ID

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when we're loading the first lists.

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All right, so that's probably
enough to start with.

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So let's go ahead now and
create DataListbox class

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and I'm gonna add this
after this Scrollbox class

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that we've created in the jukebox.py file.

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So I'm gonna add the customary two lines,

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two blank lines between classes here,

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and we're gonna start
with class DataListBox,

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and in parentheses, it's
going to be Scrollbox, colon,

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enter there, a space, and
then we're going to define

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our init method, so def, space, __init__,

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and I'll just select that automatically.

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The first parameter in parentheses
was added automatically,

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self, but we want these
other arguments now,

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so comma, space, window,

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comma, space, connexion,

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comma, space, table,

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comma, space, field,

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comma, space, sort_order

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equals, and two
parentheses, left and right.

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Then lastly, comma, space,
and then star, star,

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K-W-args or kwargs.

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All right, and I'm just gonna
put in, in a comment here,

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what the code would be for Python 2.

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Scrollbox.__init__(self,
window, **kwargs),

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and something there for Python 2,

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just so if you're following
along with Python 2,

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you'll know what to do there.

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All right, but in our case,
we're going to do a super,

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parentheses, dot __init__,
and we're gonna pass

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to this super call window and **kwargs.

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Next, we're going to
do self.cursor is equal

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to connection.cursor,

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or call to the cursor
method, to be more precise.

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We've got self.table is equal to table,

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and self.field is equal to field.

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Let's just move this up a little bit

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so we can see what we're doing here.

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And we wanna build a SQL
query now, so self.sql_select

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is equal to SELECT in
double quotes with a space,

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plus self.field,

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plus, double quotes, comma, space, _id,

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end of double quotes, plus
another set of double quotes

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with the word FROM with a
space around the word FROM

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plus self.table, and then
we'll put if sort_order,

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colon, and then we'll do
self.sql_select is equal

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to a space with double quotes with a space

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around the text, ORDER
BY, that we're adding,

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plus, then in single quotes,

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comma, .join(sort_order)

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and then we'll put an
else: otherwise for that.

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It's going to be
self.sql_select equals ORDER BY

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in double quotes with a
space around both terms,

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at the start and end, in other words,

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plus self_...

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Sorry, self.field.

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I'm gonna put another line
there to keep Python happy

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with the method, the function
that we've got below that.

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All right, so starting off
here, out init method is calling

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the super method for
Scrollbox, and I've included

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the Python 2 syntax on
line 29 as well for that.

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So next, we create data attributes

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from the parameters
passed to the init method.

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Now, we're going to work with a cursor

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so we store that rather
than the connexions.

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You can see here, we're
storing the actual cursor

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and not the connexion on line 32.

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Now, you should write a
class to accept a cursor

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rather than a connexion, but
it's probably more useful

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to provide a connexion.

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Now, I call it the column parameter field

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because we're working in the
grid layout_manager down here,

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and column could then get
confusing for that reason.

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And table of course is the table

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that we're going to be
selecting the data from.

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Now, the sort_order argument
here, we have to find that

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as a tuple to allow the caller

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to specify multiple columns
to sort on if they need to.

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Now, this doesn't make a lot
of sense with our tables,

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but if we use the view, for example,

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from the previous videos,
then it could get useful.

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And we're also trying to
make the classes as general

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as possible so they can't be
used in other programmes that

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perhaps have got more complicated
database schemes in place.

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So the sql_select attribute's
pretty straightforward,

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if you're reading that from line 36.

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Just contains a basic select statement

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to retrieve the required
field and the row ID.

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Now, we're putting a
restriction on the database

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that our class will work with.

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The table must have a column called _id.

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You can see that in here on
line 36, and that's of course

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used to uniquely identify
each row on the table.

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And actually that's not
unusual, but if you wanted

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to remove that restriction,
then you could request

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a primary key field as another parameter.

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We will not be doing that here.

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Now I've actually made a change here,

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so what I'm going to do is that's gonna be

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if sort_order, that actually
should have been if sql_sort...

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I'm confusing myself here.

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Sql_sort for that as well.

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So what I was trying to do
there is specify a SQL sort

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attribute with an order by
clause, and we're catering for

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the fact that they may be
passing that sort_order or not,

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so we're going to default to
the field and order by that

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if I don't pass a parameter
with the requested sort_order.

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Now, you could leave the default blank

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so that the data isn't sorted at all.

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That's the sort of detail you decide

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when designing your classes,

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and as long as the users
are aware of how it works,

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then that would be fine.

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Now, I'm not including doc
strings in the classes,

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because that would make
the videos too long,

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but that would certainly be
something you should add,

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especially when creating classes

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that should tend to be reused.

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All right, and again, in
the case of a sort_order

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being passed, we're using
.join with the sort_order

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and separating them by
commas as is required

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to fulfil the syntax for
an order by clause of SQL.

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All right, so the class at the
moment doesn't load any data,

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so we need to implement the requery method

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that it's going to need.

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Now, if we're going to allow
the listboxes to be requeried

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so that they can show new
data, we need some way

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to clear the existing data
out, so for that reason,

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we're also gonna add a clear method.

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So let's go ahead and add those.

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So we'll start with the clear method.

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So def clear, and of course self

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is the default parameter there, argument.

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Then we'll do a self.delete,

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in parentheses, zero, comma, space,

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tkinter.END, uppercase
letters, and right parenthesis.

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And the next one we want
is the requery method

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that we just talked about, so def requery,

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and argument is self again,
automatically added by IntelliJ.

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Then we're going to print

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(self.sql_select + self.sql_sort)

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for debugging purposes.

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But what we're going to do

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is put a TODO delete this line

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so we know to come back later

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once the testing is
complete and remove that.

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And in terms of what we're going to do now

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is from our requerying, we
first clear the listbox contents

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before re-loading, which would make sense

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so we haven't got duplicate entries.

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So we do a self.clear
to call our clear method

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that we just defined on line 43,

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and I just remove one of those lines.

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And after self.clear,

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then we're gonna put for
value in self.cursor...

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Oops, that should have been cursor.

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Then we wanna do self.insert,

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and the argument is gonna be tkinter.END,

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comma, space, value,

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and the value zero in square brackets,

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then end of parentheses.

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So the clear method, as
you can see on line 42,

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and the code's on line 43,
that uses the listbox delete

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method and we're specifying
the entire range of values,

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going from zero to tkinter.n constant,

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and that constant represents
the last item in the list.

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So consequently, calling that

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will actually delete all the entries.

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Now, the requery method that
we've defined on line 45,

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that's where our SQL statement's built up,

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from the sql_select part as
well as the sql_sort part.

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So I've printed that out,
but the other thing we need

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to do is actually add that,
so I'm talking about how it's

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being added, but we haven't
actually done that yet,

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so it's gonna be self.cursor.execute,

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and it's gonna be
self.sql_select + self.sql_sort.

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So obviously we're
printing it out on line 46.

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Line 47, we're actually
executing the combination

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of the sql_select that we've
generated on line 36 up here,

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then the sql_sort that we're creating

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on either line 38 or line
40, depending on whether

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that argument's been
passed for the sort_order.

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So then we're executing the SQL
code, as I said, on line 47.

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All right, once we've done that,

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the rest of this code
should look pretty familiar.

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We're executing the query

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and looping over the
cursor as you can see here.

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We're executing the query here on line 47.

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We're clearing the listbox contents

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and then we're looping
through the values one by one

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and then actually adding
each one to the listbox.

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And just a note here, on line 52,

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remember that we get a
tuple representing each row.

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Now as our query specified
the column we want

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and the ID, we add the
first item from the tuple

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into the list and that's
why we use the value zero

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in the square brackets to
indicate that first value.

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So at that point, that
should actually work.

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So we should be able
to test this class now

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before the video ends, so
let's remove all the code

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to populate the lists
from the artist listbox

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and replace it with a call
to this requery method

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just to check that and see
that it'll actually work.

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So to do that, we'll come down here,

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down to the setup here for
Artists Listbox on line 101.

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And what we wanna do
first is we wanna change

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the definition, so we
wanna change Scrollbox now

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to use our new class we've created,

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so that's going to be
DataListBox, and next,

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we're going to remove the SQL code here.

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And instead, we're going to replace that

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with a call to artistList.requery.

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We're just gonna be calling the code

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that we've just written.

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So let's check that first
to make sure it works.

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And we've got an error,
and of course the reason is

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we haven't specified our other parameters.

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We need to go ahead and do that.

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So we've got at the moment,
we've got DataListBox,

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we've got mainWindow, but
we also need a connexion,

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we need a table name, and we also need

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the column that we want to be displaying.

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So, we'll add those.

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So comma, space, conn, for the connexion.

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Comma, space, artists in double
quote, being the table name,

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and comma, space, name,

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being the actual field or column.

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And there's another option
there for sort_order,

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but we're not going to add that yet.

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We can add that option in later,

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just to see that it does work.

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Let's go ahead and do
that and run that again.

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This time, you can see we've
got the SQL printing out,

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and if we go back and
have a look at our code,

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we can see that we have
got our artists populated,

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so it is working now, which is fantastic.

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All right, so let's continue on now.

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Close that down.

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All right, so now that we've done that,

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we should be able to
replace the other two calls

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to our albums and also our songs.

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So we wanna change albumList here

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where it's just calling Scrollbox.

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We wanna change that now
to call our DataListBox

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and the arguments are going
to be mainWindow again,

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conn for our connexion,
comma, space, this time it's

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going to be albums for the
table name, comma, space,

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name for the field/column name,

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comma, space, this time
we'll add a sort_order,

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so I'm going to do sort_order equals,

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and I want parentheses,
and within the parentheses,

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we want name in double quotes and a comma,

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and we add a second parenthesis there.

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Okay, like so, and we'll
delete that line there.

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Last entry.

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Then what we need to do on the
line immediately after that,

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we wanna put albumList.requery,
and we leave the grid

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and the configures there were before,

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and we also leave the
binding as it was before.

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And lastly, for songList, we've
got the Scrollbox code here.

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We'll change that also to be DataListBox,

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and the arguments for that
will be mainWindow, conn again,

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and for the table, it's going
to be songs, comma, space,

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title is going to be
the name of the field,

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and let's also specify a
sort_order for this one,

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and we can just specify
that as track and title

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in parentheses, double
quotes, separated by a comma,

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and finish off the right parenthesis.

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And then of course on the next line,

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we need to do a requery,
so songList.requery.

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All right, so let's
actually try running this.

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You can see the three sets of
SQL that have been executed

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there for artists, albums,
and songs, and incidentally,

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there's no good reason
for sorting the songList

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on both track and title,
really other than to prove

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that the code doesn't crash
and so that we can check

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the SQL statement that we're printing out,

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and you can see there's multiple
sort_orders quite happily

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separated both with a comma
and made that valid code.

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But importantly, let's just
actually check this works.

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And you can see that we've
got it all working nicely.

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And now all three Listboxes at this point

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are now showing data,
which is what we wanted,

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and again, the SQL output
that we've got over here,

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I'll just move this
over, looks fine as well.

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So that's actually pretty cool.

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With subclass of tkinter.listbox
to reduce our scrollable

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listbox, and just to confirm,
we have got scrolling enabled

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for all three listboxes there,
so that's working nicely,

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and we can now load that data

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from a database table as you can see.

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Working pretty well.

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But we're still not done at this point,

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and in the next video,
we're going to add the code

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to allow our DataListboxes
to be linked together.

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Then, when we select an item
in one list, the related

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data will show in another
like it was doing earlier

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before we made the change to
move over to the DataListbox.

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But let's work on that in the next video.