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SPEAKER: Let's make some
money in CS50 Finance.

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In this problem, we
will create a website

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that allows users to sign
up, register, and log in

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in order to buy and sell stocks and
shares that they're interested in.

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Now, there's a lot of
distribution code in this problem.

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So before we go into our to-dos,
let's open the distribution code

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and walk ourselves through.

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Within these folders you'll find Python
files, HTML files, CSS, text files,

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even a .db file.

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So we need to understand how
all of these files and functions

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interact with one another, and how do
we use all of the functions provided?

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Let's open up application.py first.

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You'll see that, at the top, we
import a lot of packages and modules.

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This will allow us easier functionality
as we progress through this problem.

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Now, whenever a website makes
a request from the server,

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we are going to ensure that it actually
fetches from the server as opposed

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to going into the cache so that
we get fresh data every time.

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See if you can find
where this is located.

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Then we'll configure the Flask
section and the CS50 library

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in order to use the SQLite database.

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Now, we only want registered
and logged in users

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to access certain pages
of our web site, so that's

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where login_required will come in handy.

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Go back to the relevant
sections in application.py

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and see if you understand
what's going on.

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Within application.py you'll find
that login and logout are implemented,

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as well as apology and db.execute.

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Now even though login and logout
are already implemented for you,

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it's going to be important
to understand how

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they work because it's going to be
quite useful to use these as frameworks

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as we complete the rest of the problem.

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It's also important to understand
how apology and db.execute are

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used because we're certainly
going to be using these functions.

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Another thing that we'll be
dealing with a lot in this problem

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is form submissions via HTML templates.

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How do we retrieve that information?

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Well, within the templates folder,
we'll have our HTML template file.

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So within the HTML, if we specified
the name of our input box,

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then within Python we can
request that via request.form.get

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and then entering the name
of that input in order

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to retrieve that as a variable.

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Now let's look at how we might
execute a query to our SQL database.

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Here, I'm selecting the column
cash from the user's table

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where the given condition
is that that ID of the user

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is the ID of the user
that's currently logged in.

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Now db.execute will
always return a list.

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So even though we know that there's
only one row that satisfies this given

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query, it will still return us a list.

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So we'll have to access the
first element of that list

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to get to the relevant row, and then
we can access the "cash" index in order

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to get that value.

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Once we're a little more
comfortable with application.py,

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let's move on to helpers.

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Within helpers.py,
we'll find apology that

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allows us to essentially render error
messages to our user, login_required,

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which we've talked about
already, and lookup.

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lookup is a function that
will use an API in order

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to return us a dict with three keys,
the name of the share that we're

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inquiring about, the current
price as well as its symbol.

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Then, finally, we have usd, which
allows us to format prices nicely.

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Now let's move on to templates.

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The templates folder
currently has three files--

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apology, layout, and login.

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So we need to figure out
how these templates interact

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with their respective routes
within applications.py.

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Now, we will be adding additional
templates to this folder.

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So take a look at
these three HTML files,

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and figure out how they interact
with their respective routes

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within application.py.

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There is even more
distribution code to look into.

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So take a look at requirements.txt and
the styles.css file, which, by the way,

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you're free to edit yourself.

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Once you're comfortable with all
of this distribution code, let's

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start making our website.

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