WEBVTT

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This is looking great and
Monty Python thinks so, too.

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I showed a demo to the group and

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they realized that they forgot
to include a requirement.

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They forgot that there's a service
charge involved with each transaction.

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You can't sell tickets without
a service charge, right?

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Now this works a little differently.

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Each purchase, not each ticket,
has a service charge of $2.

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Every time you demo your software,
users will request additional features.

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It happens all the time.

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This is why it's important to get working
software in front of your stakeholders.

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This is actually a good chance
to take a look at our code and

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see if we can't refactor it a bit
to make it more easy to read.

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Well, there's a term we haven't
touched on yet, refactor.

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Refactoring is when you take a look
at your code and you improve it for

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readability or extensibility without
changing how the program actually works.

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Let's see if we can't refactor that
price calculation into a function and

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then add this new service charge.

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Okay, so I'm gonna go ahead.

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And I'm gonna add a new card.

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And this one is As an owner,
I should receive,

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A service charge so that I can pay

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others to maintain the software.

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I suppose that makes sense, right?

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Maintaining software can be
super difficult for clients.

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Now, if there's an error,
they'll need to pay developers somehow.

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So, I hope some of that service charge
makes its way to fellow developers,

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cuz it might not be us that fixes it.

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You might pick up an application that's
already working and you need to fix it.

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So, let's move this into In Progress.

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Okay, so, I'm gonna get rid of these
comments here, get rid of that one, and

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that one, and that one.

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Okay, looking good, all right.

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So let's first refactor our
calculation into a function, right?

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Cuz currently, we are calculating.

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Where are we doing that calculation?

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Right here,
num_tickets equals times TICKET_PRICE.

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So let's go ahead, I'm gonna cut this out.

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This is Cmd+X, or Ctrl+X.

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So now it's in my clipboard, it's gone.

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And I'm gonna add a function
that we'll create here in a bit.

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And it should calculate the price
of how many tickets there are.

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So sounds like a good name,
calculate_price.

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And we're gonna pass in
the number of tickets,

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which we know is a valid
number at this point.

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Go ahead and save that.

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And I'm gonna up here to the top,
and here we go, let's do this.

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Create the calculate price function.

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Let's use the proper name there,
calculate_price function.

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It takes Number of tickets and

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returns, what do we have here?

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num_tickets + TICKET_PRICE,
let's make a new.

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Cool, so create that function,
and return that value.

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All right, you got this.

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Pause me and create that function.

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Remember, it needs to take
the number of tickets.

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All right, so here's what I did.

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So I defined calculate_price.

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And I required a parameter
of number of tickets.

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I need a colon, open that body up, and
there is no need to create a new variable.

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We can actually just return the result,
right?

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So we're gonna return and let's get lazy.

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This, paste this here, but
note that this is number of tickets.

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So I'm gonna say number_of_tickets.

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Now, note how this refactoring puts this
calculating price into a separate area

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than where this loop is at there.

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So this loop will never
really need to change.

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We can figure out what this
calculation of the price is.

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And other people could use it too,
should they need to.

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We didn't need to do this but
we refactored and

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things should still work exactly the same.

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Let's go ahead and
let's run it and make sure.

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Hey, Bob, let's get 2 tickets.

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We got 20.

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Yes, I wanna proceed.

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98 tickets left, awesome, perfect.

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So now that we have it refactored,

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what we should do is we need to
add this service charge, right?

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So I'm just gonna go ahead,
I'll put it in here.

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And we need to create a new constant for

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the $2 service charge.

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Remember, that's once per transaction.

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And then we want to add
the service charge to what's due.

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Okay, you got this.

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Pause me and give those a go.

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You ready?

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Okay, so here's how I did it.

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So this service charge, I'm gonna
go ahead, I'm gonna come up here.

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I'm gonna make a new constant.

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And I'm gonna put it at
the top of the file.

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If you ever look in here, the service
charge, if we start charging too much for

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our developers,
we need to bump this price up.

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We just bump it one place here.

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And then,
I used it in the calculate_price function.

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So I'm gonna get rid of this comment here,
bring this back up.

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We can just say + SERVICE_CHARGE.

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You know what,
I'm gonna think about my dear Aunt Sally.

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And I'm gonna use some parenthesis
even though I don't need to.

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Because I know that multiplication will
happen first and not the addition.

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But I'm gonna do that cuz I think
that that makes things more clear.

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Let's go ahead and see how we did.

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I would like to have 2 tickets.

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$22, because of that service charge.

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And there we go, great job.

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Now I do like how if they
change the way that this works,

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we know where to change things.

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It's right up here at the calculate_price.

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And when you look at it used in this
loop here, it's pretty clean, right?

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It's really clear that the price
calculation is happening elsewhere, and

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we don't need to worry about it here.

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If you wanted to calculate
this on a different page,

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on like a shopping cart page,
you could use that same function.

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It's reusable, we change it in one place.

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And you know what?

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I think we're done.

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Awesome job.

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I want you to take a minute and
breathe in this program.

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Look at all the tools that
you stitched together.

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You really have learned a ton and you
were able to build an entire application.

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You did an excellent job at
immersing yourself in the Python

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programming language.

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Excellent work.