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You have completed Python Basics!
You have completed Python Basics!
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Let's catch a couple of exceptions and raise one of our own.
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I'm going to clean up these comments,
they're getting a little busy,
0:00
these instructional ones.
0:03
So we'll get rid of this,
so I'm using again,
0:04
Command + Shift + D to
delete some lines here.
0:07
Let's bring this up.
0:10
Don't need that anymore,
don't need that or that or those.
0:12
Let's get rid of that,
0:16
I'm going to leave that to-do because
we definitely need to do that later.
0:17
Get rid of this.
0:21
Otherwise, and thanks.
0:23
Sold tickets.
0:25
This line, there we go.
0:27
And it's actually 20 lines of code,
awesome.
0:28
That feels better.
0:32
I'm gonna save it, and now,
when we get this cleaned up,
0:32
should we walk this real
quick with those missing?
0:37
Remember, that we are on the,
as a user I should have errors reported in
0:39
a user-friendly manner,
which is kind of always the case.
0:43
But we really wanted to make sure that
we handled this cuz they saw one of
0:46
the tracebacks that I left earlier.
0:49
So all right, here we go.
0:51
First off.
0:53
So here, we have a constant and it's in
all upper case, it won't change while
0:53
the program's running and if the group
wants to change this in the future,
0:58
it's a very easy place to change it,
constants.
1:02
So these are how many tickets
are currently available, now note,
1:06
it's not all uppercase.
1:11
So we can assume that
this is going to change.
1:13
And then we have, while there is one or
more tickets remaining.
1:16
Okay, we're going to keep on
living through all this code.
1:21
So we're going to show how many are left.
1:25
Then we're going to grab their info,
what's your name, how many tickets,
1:28
we're going to coerce that.
1:31
Because input always returns a string, but
1:33
we need to use num_tickets for
a math purpose.
1:36
So we definitely need an integer.
1:39
Now, it's an integer because you
can't buy fractions of a ticket.
1:42
I'd like to buy one and
a half tickets please, that doesn't work.
1:45
So if you remember, this seems
a little bit dangerous, doesn't it?
1:48
What if the user gave us
something that we couldn't coerce?
1:52
Let's keep this in mind for
a possible problem.
1:56
Okay, and then we calculate the price.
1:59
And then we show them the total.
2:02
And we ask them, yes or no,
do you want to proceed?
2:04
And because we aren't sure if they
are going to use an uppercase Y or
2:07
lowercase in responding, we lowercase it.
2:10
And we check.
2:13
We left a nice to-do message here that
the SOLD is not really taking any credit
2:15
cards, and then we subtract the number
of tickets from the tickets remaining.
2:20
What would happen if the user
entered 1,000 tickets?
2:26
Whoa, that'd be negative
900 tickets remaining.
2:30
The while loop up here,
this would stop, right?
2:34
Cuz it'd be negative 900, that would stop.
2:36
It's not greater than or equal to one, but
2:39
still, the 1,000 ticket
sale would go through.
2:41
We've got to catch that, right?
2:44
So and then finally,
anything other than y,
2:46
we're going to say Thank you anyways, and
we're going to be friendly about that.
2:49
And then we're going to let people
know that those tickets are sold out,
2:53
because the loop's over.
2:56
So once that loop's over, they know.
2:57
Did that feel pretty good being
able to read most of that?
3:00
That's pretty cool, right?
3:02
Pretty amazing.
3:03
All right, now,
let's take care of these errors.
3:05
Let's do one at a time.
3:08
So the first problem that we have is here,
one around coercion, right?
3:10
So remember,
the user can add anything here.
3:15
So let's run it to see how
bad the errors actually are.
3:17
I want to clear this.
3:24
Let's run python masterticket,
and our name is Gallahad.
3:26
How many tickets would you like?
3:33
Blue.
3:35
Blah, what a gross error.
3:36
And our program ended.
3:39
We can't have that happening.
3:41
We won't be able to sell anything
more if we drop out like that.
3:42
So it throws a ValueError.
3:45
I'm gonna go ahead, I'm gonna copy that.
3:49
And right above here, right above
int( num_tickets), let's say expect,
3:55
I'm gonna paste a ValueError to happen.
4:00
And handle it appropriately.
4:04
Let me give you a hint,
remember to test it out.
4:12
Pause me, and give it a go.
4:16
Are you ready?
4:17
All right, ready?
4:19
This is how I went about fixing it.
4:21
So I definitely needed a trial block.
4:22
So I did the block here and
we wanna be careful about the num_tickets.
4:25
And I want to accept,
we know that that throws a ValueError.
4:33
And what we wanna say is print,
4:38
no, we ran into an issue,
4:44
please try again.
4:49
Now, that feels good, doesn't it?
4:52
But I'm gonna go ahead and run this.
4:54
My name is Gallahad and I would like.
4:57
How many tickets would you like blue.
5:01
Total due is blue blue blue blue blue.
5:04
What?
5:06
How is blue blue blue blue blue.
5:07
Yes.
5:11
Remember, this is where the error happened
and the assignment never happened.
5:13
So num_tickets here is the string blue.
5:17
And because you can multiply strings,
5:21
right, repeat the same
thing a number of times.
5:24
This repeated however marks
the ticket price was which is ten, so
5:26
those are ten blues right there.
5:29
So in order to fix that,
I need to put this code in an else.
5:33
Cuz we only want this code to run
if we know how many there are.
5:40
So let's do this, and I'm going to
indent it with command right bracket.
5:43
Then let's go ahead, and if you want
to ever stop out of a program while
5:51
it's waiting at a prompt, you can do a
control C and it will send this interrupt.
5:55
So let's run that one more time,
make sure it's working.
6:02
My name is Gallahad, blue.
6:05
It says, no, we ran into an issue,
and then it just keeps on looping.
6:09
There's 100 tickets remaining, awesome.
6:11
Okay, now we have another error,
too, don't we?
6:13
We don't want to allow for
that 1,000 ticket sale, right?
6:15
We need to block that.
6:18
So why don't we do that
in the try portion here?
6:20
So if we come up here into our try,
6:23
we wanna make sure that we have a valid
number of tickets to request, right?
6:27
So we will raise a ValueError
if the request is for
6:31
more tickets than are available.
6:39
And then I wanna make sure that that's
a user friendly error that we raise.
6:44
So what I want to do next is I
wanna include in the output here,
6:48
we want to include the error
text in the output.
6:55
All right.
7:01
Remember, you can lean on the community.
7:02
And also, you can rewatch the previous
video where we did something similar,
7:04
check the Teacher's Nets.
7:07
You got this.
7:09
Are you ready?
7:10
Pause me.
7:10
Ready?
7:12
So here's what I did.
7:13
So I used an if statement up here.
7:14
So I said, if the number of tickets,
that's what they asked for is greater
7:17
than the tickets_remaining, you can't
do that, you can't buy those tickets.
7:21
So, what we did was we
raised a ValueError.
7:27
And I'm gonna go ahead and
be very specific, there are only,
7:33
use a placeholder here, tickets remaining.
7:37
Nice try.
7:43
So then we'll do format and
we'll say tickets remaining,
7:45
and then we'll do a closing.
7:53
Okay, and
then if I want to use that exception,
7:55
you have to use the as keyword,
did you remember that?
7:58
If not, don't fret,
we only did that one time in this course.
8:02
The more you practice,
the more you will be able to recall it.
8:05
So, you have to use the as keyword,
so as err.
8:08
So, no, we ran into an issue, I'm gonna
go ahead and drop our message there,
8:12
then I'll, was that a period,
space, please try again.
8:18
And then we will format that
with our error, format, err.
8:22
There we go.
8:27
Okay, I'm going to break out of this,
8:31
I'm going to clear this and
run it one more time.
8:33
What is your name?
8:38
It is Sir Robin.
8:39
I would like 10,000, no we've ran into an
issue, there only 100 tickets remaining,
8:41
please try again,
there are 100 tickets remaining.
8:46
Awesome, so I think we can
move this final ticket over.
8:50
How good does that feel?
8:57
I am gonna go run a demo for
Money Python and see what they think,
8:59
they're gonna love it,
I know they're gonna love it
9:03
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