WEBVTT

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ok so moving on what will do now in the deal_player function

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is will just add that command that we saw in the
previous video to print all the local

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variables just so we're 100% clear on which
variables are local to the deal_player

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function so you can do
this right down here at the bottom will do

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a print out....and that is going

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to do just that print a list of all the
local variables so if we run the program

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now and go back to our game that is
running click the player function and

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you can see card_value which has a score
of 10 or value of ten and player_score

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which also has a value of ten
they are he 2 only local variables in this

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function so it can really be useful because any
confusion in your programs to use this

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locals function to call just so you are aware
fully which variables are local ok and it

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just bares repeating the rule again one
more time when you use the name of a

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global variable inside a function Python
is going to use the global variable as

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long as you don't assign a new value to
it as soon as you add code that tries to

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change the value the variable itself
becomes local and shadows the global

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variable with the same name so because
the function assigns the value in

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this case 0 to players_score I'm talking
about the code on line 47 player_score

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becomes local to the function and
because no values was assigned to player_ace

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we've only used the value we haven't
actually stored anything in there it's still

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refers to the global variable that also
means that you can have a function that

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happily using a global variable but will
suddenly switched to being local if you

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happen to add code to change the value
of the variable and that can be really really

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a gotcha their that will start potentially unpredictable
things or giving you unpredictable results

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in your program now the
deal_player function provides a

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good way to see this in action because

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should actually change the value of
player_ace and looking at the code on

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line 50 the card values is set to 11 if
this is the first ace dealt so if that

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is the case then what we really should
be doing is setting player_ace the

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variable player_ace to true so that
we know that there is a ace with a

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value 11

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so similarly you should also set to false when
we subtract 10 from score on line 54 so

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if you go ahead and add it to line 50 so up here
and we put....

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now immediately we gonna get an error well
two things happen when we did that

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there's an error on now on line 49

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and also IntelliJ is now warning  about player_ace
shadowing the global variable

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of the same name so the errors is unresolved
reference player_ace and this can

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be confusing probably thinking well hang on
player_ace tim you've just told me

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that that's a global variable why isn't that
working well again because we've assigned a value

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assigned a value now on line 50 what's
actually happened is its now being

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converted into a variable a local variable
for this method and on line 49 when we're

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doing a test for the value it hasn't
been initialize it hasn't been created as

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such and it doesn't exist so that's
its coming and saying unresolved

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reference to player_ace and
the other era in terms of the shadowing

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name well we talk about that extensively we
know why that's coming up and that's

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just because we're using the same
variable name of the variable in the

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global variable as we are in this case
in the local variable so deal_player wasn't working

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function but as soon as perfectly valid
assignment on line 50 was actually added

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then we started getting an error now before you actually gone

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through this video this type of error would
probably have driven you nuts now though

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you can see why the IntelliJ
warnings are coming up and immediately know

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what's going on so in a while what I'm
gonna do is rewrite the function so that

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it doesn't try to make use of global
variables ideally a function should be

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self-contained and not make changes to
anything outside itself now when a

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function does change things like

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global variables the changes are know as side
effects and it should really be avoided

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wherever possible but with that said sometimes
side effects

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are necessary so they are allowed but
aren't discouraged Python

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automatically changing a global variable
to local when you try to change when you

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try to change it is Python's way of
discouraging us from doing that because

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they are occasionally necessary Python does
provide a way to make changes to global

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variables within a function because of course
this is what the problem is here we

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actually on line 50 when it change the value
of a global variable and it's not

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allowing us to do that because as soon
as we've type in the same name and type in

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an assignment to save a value to that variable it's created a

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local variable and then consequently in
this case we got an error saying that

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as of line 49 that variable didn't exist so how
do we go about changing a global

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variable well the way to do that is to
specify that your intent on using global

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variable by using the global keyword but
before doing that let's get rid of the

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error on this line that sets player score to 0 every time the function is

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called because that shouldn't be there this
is the code on line 467 because we really do want to use the

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the score actually saved globally so
let's go ahead and delete that and as soon

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as we have done that you can see now their are other errors on line 51 53 54 55 and 56 their is now errors

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relating to player_score so
before I hover over and show you what the

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error is and taking into account what
I've said in the video the mini challenge

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for you is to answer this question and it's
why is now their an error when players_score

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is being accessed and the hint
here is that we've talked about this

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player_ace so have a think about that pause
the video and try and figure out why

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we're getting an error with player_score now and when we come back i'll go through that with you

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ok hopefully that made sense in terms of why that error
came up and what it is it's really the

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same reason that player_ace returned an error and of course I talked about

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that earlier in this video so by
removing the assignment that I did when I

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deleted line 47 player_score now
doesn't have a value as far as

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this functions concerned and this is just
primarily because we're trying to save

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a value into player_score so as of the code on line 51 player_score

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doesn't exist as a variable
because of the shadowing functionality

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that Python does that the local variable
variable hasn't been initialized and

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that's why we are getting those errors again
similarly to what was happening with

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player_ace and specifically the
augmented assignment like we're seeing

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on line 51 requires that the variable
already has a value and of course because

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of the shadowing technique Python knows that
we're using a variable of the same

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name and it's trying to create it would normally create a local variable but we

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haven't actually done that we haven't
initialized that variable at this point

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in time because their assignments
player_score is still a local variable

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but of course we just deleted the line
that gave it a value ok so enough talks so how in

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other words do we get the function in
this case to use the global variables of

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the same name well to tell Python we want to used the
global variables we just use the global

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keyword at the start of the function so
we came up here and on line 47 I'm gonna add

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global.....and what that immediately

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tells the function to use is to use the
global versions of those variables and

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not trying to create a local
variable of the same name and consequently

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all the errors  disappear at that point in
time and also the

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the errors about shadowing or the warnings about

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shadowing have also disappeared as well
because in fact we're not shadowing

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anymore because the global keyword essentially is really as I said

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telling the function to use the global
variables from this point forward in

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that function so now if we run the
program again and actually I need to make another

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change so just close it down

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before we do that because we needed to make the
change here to add player_ace =

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false

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so when we are deducting 10 from the ace if you
recall we need to actually say....

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.....so basically if the
card value is 1 in other words an ace and they haven't already

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got an ace then we're going to assign
the player_ace variable which now global to

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true but in the case of where there was
an ace their was an ace being treated as a

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value of 11 and we've detected 10 from
it then for all intent and purposes we haven't got

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that ace any more we are setting it back to false so now we should be able to run this and now when we run it

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we click on player a value of ten their value of
twenty and one more and we get the

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right message correctly coming up now
saying dealer wins so it's obviously

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working out clearly it's using the
global scope and just make sure this is

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working and it's random running game again
their is an ace 11 oh we got 21 we got blackjack now obviously

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we haven't got a calculation in here to
check for blackjack we actually only

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doing the score here score check if the
player scores greater than 21

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we are not basically figuring out whether the
players won yet and we should bust

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and if we click on one now it is clearly it's just
drawing random cards so its all working nicely

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so what we've determined now is that Python
does allow

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global variables to be modified inside a
function because of course that was the

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problem we're always been able to get
access to global variables but we're

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talking specifically about changing
those variables changing the values to

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do that in a function you need to use
the global keyword that I've

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shown you how to use on line 47 through 48
so the functions now working as we saw

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when we ran the game but if this functions
modifying the two global variables player_score

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and player_ace how can we will be
sure that some other function isn't also

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changing them and its quite possible when a game in that could happen and if something else

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does change them then the deal_plater function is no longer going to work

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correctly because it really is assuming
that it's got full control over those

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variables or the way that the code has been
written and this is the main reason why

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side effects are discouraged and why functions really should only be modified

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varaibles in the outer scope i.e. globally if
there's really no other way to perform

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the functionality that are you creating
and usually there is actually way

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around so before we write in the function
to remove the side effects it is actually

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worth revisiting the design so the deal_player gets a new card and

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maintains a total by adding the value of
that card to its tally and that

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tallies now stored in player_score as a global variable

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and we are gonna have to do the same thing for
the dealers so it may make sense to

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create a function that returns a score if
it's given a list of cards so what we

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gonna do is we are going to add a score _hand function and its purpose is

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to do that it to look at a hand and
calculate a score based on that hand so

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we are gonna create that under deal_cards
so down here we are gonna call it...

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....

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....

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.....

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....because when we first

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starting we haven't got any cards so obviously
we haven't got an ace and lets go through all the cards so....

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....

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......

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....

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.....

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....

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.....

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....

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.....and that's basically the method that's the

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loop that goes through each hand then when we finish we return the
score so given a list

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containing tuples wether the first item
in the tuple is the value that function is going

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add up all the values and return the score
and as I mention the first ace will have the value 11

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rather than 1 and if the total score goes above
21 and there is at least one ace then

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the total has decreased by 10 and
hopefully the player won't have busted but in

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any case we are going to return the score so that is
pretty much the same as what we're doing

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when dealing the card and it now goes through
the entire hand rather than the single

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card at a time so now that we've done
that we can actually implement this

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in deal_player and before calling
it the card just dealt is added to the

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list that contains the player's hands so going back to deal_player

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obviously our designed has changed
dramatically so what we gonna do here is

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we are going to delete all this function well what I'll do I'll just comment it

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out so you still got access to that if you
want to but it's now a lot easier so....

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....

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....

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...and that should

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be it so basically what we're doing now
is what we've done is we've

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rewritten the deal_player function to put all that logic call

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the logic that we've just created
in the score_hand and we are still getting

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this warning about shadowing but we no
longer need these global variables

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anymore so we are gonna delete player score = 0 and player ace = false so gonna go down and delete these

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now so player_score = 0 and player_ace = false so delete those

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now because we no longer need those and the video is getting a little bit long so I'm gonna stop

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this video here and in the next video when
we come back we're going to look at the

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deal_dealer function because
that is now very very similar to the deal_player

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but obviously need to do a
test to see whether the player wins and etc

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so I'll see you in the next video