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Create a reusable function to remove calculations
This is looking great and
Monty Python thinks so, too.
0:00
I showed a demo to the group and
0:03
they realized that they forgot
to include a requirement.
0:05
They forgot that there's a service
charge involved with each transaction.
0:08
You can't sell tickets without
a service charge, right?
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Now this works a little differently.
0:15
Each purchase, not each ticket,
has a service charge of $2.
0:17
Every time you demo your software,
users will request additional features.
0:22
It happens all the time.
0:25
This is why it's important to get working
software in front of your stakeholders.
0:27
This is actually a good chance
to take a look at our code and
0:31
see if we can't refactor it a bit
to make it more easy to read.
0:34
Well, there's a term we haven't
touched on yet, refactor.
0:38
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.
0:44
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.
0:52
Okay, so I'm gonna go ahead.
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And I'm gonna add a new card.
0:55
And this one is As an owner,
I should receive,
0:57
A service charge so that I can pay
1:05
others to maintain the software.
1:10
I suppose that makes sense, right?
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Maintaining software can be
super difficult for clients.
1:17
Now, if there's an error,
they'll need to pay developers somehow.
1:19
So, I hope some of that service charge
makes its way to fellow developers,
1:23
cuz it might not be us that fixes it.
1:28
You might pick up an application that's
already working and you need to fix it.
1:29
So, let's move this into In Progress.
1:33
Okay, so, I'm gonna get rid of these
comments here, get rid of that one, and
1:36
that one, and that one.
1:41
Okay, looking good, all right.
1:44
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?
1:56
Right here,
num_tickets equals times TICKET_PRICE.
1:58
So let's go ahead, I'm gonna cut this out.
2:01
This is Cmd+X, or Ctrl+X.
2:04
So now it's in my clipboard, it's gone.
2:06
And I'm gonna add a function
that we'll create here in a bit.
2:08
And it should calculate the price
of how many tickets there are.
2:12
So sounds like a good name,
calculate_price.
2:15
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.
3:02
Pause me and create that function.
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Remember, it needs to take
the number of tickets.
3:05
All right, so here's what I did.
3:09
So I defined calculate_price.
3:10
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.
3:28
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.
3:45
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.
3:51
We didn't need to do this but
we refactored and
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things should still work exactly the same.
3:57
Let's go ahead and
let's run it and make sure.
3:59
Hey, Bob, let's get 2 tickets.
4:03
We got 20.
4:05
Yes, I wanna proceed.
4:05
98 tickets left, awesome, perfect.
4:07
So now that we have it refactored,
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what we should do is we need to
add this service charge, right?
4:13
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.
4:35
Okay, you got this.
4:44
Pause me and give those a go.
4:45
You ready?
4:47
Okay, so here's how I did it.
4:49
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.
4:57
If you ever look in here, the service
charge, if we start charging too much for
4:59
our developers,
we need to bump this price up.
5:02
We just bump it one place here.
5:05
And then,
I used it in the calculate_price function.
5:07
So I'm gonna get rid of this comment here,
bring this back up.
5:11
We can just say + SERVICE_CHARGE.
5:16
You know what,
I'm gonna think about my dear Aunt Sally.
5:21
And I'm gonna use some parenthesis
even though I don't need to.
5:25
Because I know that multiplication will
happen first and not the addition.
5:29
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.
5:37
I would like to have 2 tickets.
5:42
$22, because of that service charge.
5:44
And there we go, great job.
5:48
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.
6:29
You did an excellent job at
immersing yourself in the Python
6:34
programming language.
6:36
Excellent work.
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