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The Application
8:05Let's go over the User Stories to build a shopping list application
[MUSIC]
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All right,
we've now got lists in our bag of tricks.
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We can start to make applications
a lot more interactive.
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Instead of just prompting for a single
response, we can continuously ask for
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more information and store it in a list.
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There are a lot of applications
that build lists, but
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one that I'm very familiar with is one
that builds my weekly shopping list.
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I love these things.
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I've got one on my phone, I've got a to
do list app that I use on my Mac, and
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I even use an Alexa to
add stuff to my list.
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I can't get enough,
let's make another one.
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I've already built the user stories for
it.
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All right, let's take a look at
the to do list for the project.
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I put these into user stories and
I'm using Trello here.
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Again, it's another list.
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I told you I love these lists.
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But here we go.
So as a user, I should continually be
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prompted so that I can add a grocery
item or view my list when I need to.
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So we wanna just keep on asking,
hey what do you wanna buy?
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What do you wanna buy?
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That sounds good.
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Put that into to do, we can do that.
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As a user,
I should be able to ask for help so
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that I can understand how
to use the application.
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Also always a great idea,
glad there's a ticket for that.
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As a user, I should be able
to add an item for the list.
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What good is one of these list apps
without being able to add an item, right?
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So as a user upon adding
an item to a list,
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I should know the total length
of my list so I don't go over.
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So that I don't, I'll say, let's fix that.
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So I don't over buy,
change this real quick.
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So we don't over buy or
over purchase there, there we go.
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As a user, I should be able to
see the list at any time so
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that I can verify my order.
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Yeah, we want to be able
to look at the list and
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make sure that that's
what you got going on.
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And then finally, as a user I should
be able to state when I'm done so
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that I can print out the list in totality,
that makes sense.
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Okay, so let's go ahead,
let's pick up this first one,
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let's get our loop going, right?
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So I should continually be prompted so
that I can add a grocery item or
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view my list when I need to.
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I wanna move that to In Progress.
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All right, let's flip over here.
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Let's go ahead and
we're gonna add a new file,
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we will call it shopping_list.py.
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So we want some sort of main loop,
don't we?
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There are a couple of different
commands that we need to handle.
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Now, I saw one that wants
us to show the list, and
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there's one where you can ask for help.
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And then there is another one that
lets you say when you're done.
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So we've got to handle all these commands.
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When you want a loop to run for
an indefinite amount of time,
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one trick that you can use is what
is known as an infinite loop.
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Now it's probably gonna feel a little
weird, but what you can do is this.
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You can say while True.
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Now what's strange about that is that it
would appear that whatever the body of
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this loop is gonna be,
it's gonna run forever, right?
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This is always gonna be true,
true's never gonna not be true.
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So this loop will run forever
unless someone interrupts it.
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Well, lucky for us you can do that.
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There's a keyword named break, and
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what it does is it breaks
out of the outermost loop.
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So let's do this, let's go ahead and
our first line here,
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let's take some input from the user.
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I'll just call this,
new_item, and I'll say input,
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and we'll make it generic, right?
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Cuz they're either gonna
be typing an item,
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or they're gonna be typing one of
those commands like HELP or DONE.
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So we'll make this generic,
we'll do a greater than sign there.
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All right, so let's take a look really
quick at our stories, prompt this so
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that I can add a grocery item,
review my list when I needed to.
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It's almost done.
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Let's go ahead and grab, this one here is
a good one to look at because this will
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help us show how to break out of
this infinite loop we just created.
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Let's get that so we can do that.
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So as a user, I should be able
to state when I am done so
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that I can print my list in totality.
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Let's bring that up here to
In Progress and come back.
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What we wanna have happen is,
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if the user inputs DONE in all
capital letters we'll exit the loop.
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So let's use that break keyword,
we can do that, right?
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So we say if new_item = DONE and
we're gonna use all caps there.
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What we want to have happen is we
want to break out of the loop.
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Cool, so let's give that a run,
let's just make sure that that's working.
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So if we say python shopping_list,
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we can say anything at all,
anything we wanna say here.
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But when we type DONE, boom the program
exits because we broke out of the loop.
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This loop was just running and running and
running but when we said break,
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we dropped out.
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Awesome, so
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how are our users going to know that they
need to type DONE in all caps like that?
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Well, let's look at that list again,
let's look here.
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Here it is, HELP, as a user I
should know how to ask for help so
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that I can understand how
to use the application.
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So good that that's there,
let's do that one too.
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Let's come back over.
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So I could assume that we'll probably
want to show HELP before the program
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starts, right?
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So you can kind of see what's happening.
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And the ticket says that they
should be able to ask for
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help whenever they want to so
that's also one of these commands, right?
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So let's do this, let's make a function so
that we can call it when we need it.
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So I'm gonna come up here and I'm gonna
give us some space and say def show help.
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That makes sense and
I we'll describe, I'll say print.
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So we'll show this one
when they first see it.
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What should we pick up at the store?
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And I'm going to use
a multi line string here.
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And this is really good I think for
when you wanna add some help.
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So we'll come over here, so
remember, you can do multiple lines.
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So we'll say Enter DONE
to stop adding items,
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and Enter HELP for this help,
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this help was shown right here.
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So then I'll close that off, and
I will close the print statement.
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Awesome, and we'll call it, right,
when the program starts, right?
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Why not, we'll say, show_help.
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We'll call that and we also want to show
it if our user types that command, help.
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So I guess, elif new_item = HELP, so
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if they do = HELP, we'll do show_help.
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And we don't really want
the rest of this loop to run,
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no matter what's happening down here.
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We have completed what we need to do for
this thing on the loop.
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So one thing that we can do,
which is along the same lines of this
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break keyword,
is to use the continue keyword.
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So continue makes the code jump back
to the while statement immediately,
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like none of the rest of
the code in the loop will run.
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It will jump right back up to
the while true line there.
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So break breaks out of the loop, and
continue completes the current iteration.
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So I think we should add it here, right?
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Since we want it to come back to
the prompt the soonest help is shown,
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we don't really know what's
gonna happen below this.
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But the job for this specific
iteration of the loop is done already.
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So let's go ahead, and let's say continue.
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Awesome, cool, so we'll do clear and we'll
give this a run, Python shopping list.
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There is our help,
that looks pretty good doesn't it?
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So we can say blah,
blah and I can type HELP.
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Hey, there's our help again,
and I can type DONE.
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There we go, and with that let's move
some of these tickets over Done.
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So continually prompted
definitely happening.
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As a user, I should be able
to state when I am done so
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that I can print out the list in totality.
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Let's leave that one running so
we can remember to print out the list.
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Cuz there's a little bit
of a gotcha in there and
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we wanna show the list when we're done.
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But we don't even have a list yet.
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So I'm gonna move this one over too,
ask for help, so that you can use it.
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We're increasing, and we're gonna keep
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this Done ticket alive because we haven't
even created the actual list yet.
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Let's change that right
after this quick break.
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