WEBVTT

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ok so moving on with our blackjack
program now just before we continue their is a

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few items of housekeeping that
I want to go through firstly when we actually run

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the app I've mentioned before that it wasn't
sort of looking the best so if I have

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look and run it you can see that there's a lot of
white space and obviously as we start

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using it it gets better and the cards get
dealt

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and its starting to take up some space so
probably the easiest thing to fix right

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now is just a change this backgrounds so what
I'm going to do is change the background

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so its green so that's number one

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go ahead and do and where I would do that
would be just under the two lines that

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set the window title and the geometry
now here I'm gonna type....

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...and if we run that we've got a green window that's going to look

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a little bit better once we've got some cards in there so that's number one that has made our application

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look a bit nicer and bearing in mind that we haven't

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got an text showing here but that will be becoming
but the other issue that I want to fix

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is this code on line 8 its really in the
wrong position that's should really be the

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last line of codes so I'm going to actually
move that down delete that line and

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then put it down right below all the
other definitions I'm going to put it

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down here and will be actually dealing
with talking about this a little bit

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later we're going to talk about an idea of a main function to put the code

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that's not directly in functions but we will
be doing that a little bit later and lastly

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on line 35 you may recall that I
talked in the previous video about making sure

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when we're actually grabbing cards the
that we don't pop the cards of the end of the list

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and that's what I did so next_car = deck.pop on line 35 is doing just that

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so we don't want to grab a card from the
bottom of the deck

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we want to grab a card from the top of
the deck obviously so that's a mistake on

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my behalf that should actually be a 0 their 0 meabs to pop it basically to grab the

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card that's sitting from the top of the
deck that's obviously the card that we

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actually want to grab ok so now that we've
done that we've finish off that bit of

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housekeeping the next thing we really
need to do is calculate the players

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score and displayed in the frame that
is in that little bit at the top of the screen

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that I pointed before now I want to
demonstrate the other reason why IntelliJ

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gives warnings about local variables
shadowing those from the main program

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of course we talked about shadowing in
previous videos and so the first attempt

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at running this function isn't going to
be the final one so although I'll be

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replacing this first line of code the
technique used is sometimes necessary so

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it's really important to understand it
and the reason for these warnings so in

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terms of the players scored the
sensible place to calculate the total is

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just after each card has been dealt so what
I'm gonna do is modify the deal_player

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function this is one
starting on the on line 46

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so the face value of a card can be
obtained from the tuple returned by the

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deal_card function so that
can be used to update the players total

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now the code also has to deal with the
two values that an ace can represent so

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in blackjack that's not actually too
difficult luckily because no matter

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how many aces a player has only one of
them at most can have the value 11

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of course a player will be bust because the
maximum score is 21 so the technique

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used here is to give the first ace the value 11 and add any subsequent ones the value of 1 now if

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the player goes bust by holding at least
one ace ten is subtracted from the

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total and a check for being bust is
perform again so that way it will actually

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give the player the option to treat an ace
as one instead of 11 so in order to do

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all this we actually really need two
more variables one to store the players

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total and another two to tract whether
or not the player holds an ace that has

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the value 11 so let's go ahead and add
those so come down here first

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just after the player_score_label I'm

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gonna add a line of code they're and I'm going to put...

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and also gonna set another variable.....

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...now I'm not sure if I've used this term before but
variables that are defined in the main

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part of the program rather than in a
function are called global variables and

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variables that only exist inside a function
are called local variables and I know we

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talked about that before so in this case
where I've actually added these two

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global variables on line 72 and
73 by putting them here outside of the

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function we're making them global
variables so ok now that I've actually got those 2

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variables set up we can go back to our deal_player function and start

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using it so I'm gonna start typing some code in so deal_player I'm gonna start by putting....

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.....

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...we are actually obtaining the result from the

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deal card function and need to do a bit of
checking here so....

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....

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...so by default and ace has got a value 1
and what we're saying here is if an ace

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was drawn from the card from the deck and the player hasn't

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already got an ace in their hand then we are
going to assign 11 to this particular

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card so next we are gonna put...

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......

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...and we need to make a change here this deal card we need to also

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make sure that we can return the face
value of the cards so we need to specify

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position 0 element 0 so basically we
are determining if its the right value and then

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were actually assigning the score so player score += card_value and will do a test here will

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put..... because we are gonna treat the

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ace as one if the total score is over 21
so put....

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....

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......

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......

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...so the only information
we get we can get on the outcome of the

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game is if the player goes bust and that's
because the deal were not get any more

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cards until the players finished their go so
we can set the result to the dealer

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winning if the player goes bust but any
other outcomes will have to wait until a

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dealer is getting cards now before going any
further I'm going to run the program and you can

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see that sort of behaves but there is a
subtle bugs ok so just have a look at this running

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now so if I click on player notice that the
score is being updated but if I click it

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again and noticed it's only storing the last value

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so its not actually calculating the total and reasons

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for that its going to be probably be pretty obvious if
we actually closet this and have a look that's

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because on line 47 we used a local
variable and overrode

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the global variable and set it to a value of
0 so consequently the player_score is only going to ever

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be the total of the last card that was
actually drawn now just before we go

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ahead and actually removed that and fix that error if we
just have a look at the error shadow name

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players score from out of scope the shadowing of

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player score is one of them the other is
that why don't we get the same warning about

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player ace because both variables
are defined in the main program but

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IntelliJ is really only warning about
one of them in the deal player

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functions so why is that the case so lets
actually do a bit of a mini challenge for you

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is looking at this method is
there a difference in the way that

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player_score and player_ace
are used in this function and that might

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lead to why IntelliJ is only warning about
player_score so stop the video now

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and see if you can figure out the difference between
player_score and also player_ace

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and also how they are used in this process
and if you think you got it come back and we'll continue

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on

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ok so hopefully managed to figure it out
and the answer is that the value of

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player_ace is used in the comparisons
on line 49 and 53 its being used but the

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difference between that and the player_score variables is that the

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function doesn't attempt to assign a new
value to player_ace but player_score

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is assigning new values so its first
set on line 47 to 0 and then the card value is added

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to it also on line 51 and then of course
ten is subtracted from it if an ace is held on

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line 54 and its because of this difference
in the way that they used that Python

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treats the variables differently inside each function so IntelliJ is just

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reporting here it's Python is that actually
making the rules so we can confirm that

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there is a difference by using command
click so I click on player_score and if we click it to

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see player_ace goes back to our definition
on line 83 that's control-click if

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you're on PC or Linux machine and go
back to our function again so player_score

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on the other hand If I clicked that
somewhere other than the definition its

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staying in the method itself so try again their but player_ace if I click that that

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goes down to where it was define on line 83 so that's just a quick way to determine

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local or global variable putting that function back again so when you use the

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name of a global variable in a function
Python assumes that you want to use the

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global variable and will happily let you until you try to change its value

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that's the key point there so soon as
you assign a new value to a global

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variable within a function Python then
creates a local variable with the same

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name and your cpde no longer refers to
the global variable so once you

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understand behavior it actually does
make sense and it actually saves you

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from introducing hard to spot bugs but
it can be an unexpected behavior until you

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do understand that and we can see that
in action in our deal_player

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function their now so at the moment we've used the
variable name player_score

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and assigned new values to it

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as a result Python's created a new
local variable called player_score

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and IntelliJ's complaining
by giving us a warning that its shadows

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the global variable so it is important
to pay attention to those warnings as

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they are the only clue that we really not
in fact changing the global variable

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player_score also inside the
deal_player function we use

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the variable name player_ace but we haven't
assigned in new values to it so as a

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result Python let's us refer to the global
variable and consequently there's no

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warning bells from IntelliJ about
shadowing because we in fact not doing that

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because we are not saving values and essentially not creating a

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local variable so I'm gonna end this video here
now in the next video will continue our

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discussion about this and then move on
and get this deal_player

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function working correctly in calculating

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the score for the entire hand the players
got rather than just last card so I'll see you in the next

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video