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<v ->Hi guys and welcome back.</v>

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In this video, we're going to start looking at the code

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that we're giving you for this project.

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Because we've already built a few of these database

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using command line apps, we figured it would be best

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to give you some code so that we don't have

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to write everything from scratch.

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Everything we're going to give you though,

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we already know how to write.

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We've already covered this in previous sections,

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so there's nothing new here.

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Everything that's new, we haven't written yet,

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we're gonna write that over the next few videos.

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So, let's get started.

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Here I've opened the poll project in PyCharm,

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you can download all of this starter code

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with the resources section of this lecture

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and we have a few files.

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First of all, something new, the requirements.txd

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just contains the libraries that you need

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in order to run this project.

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When you open up the requirements.txd,

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you can see the libraries you need,

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you can just go ahead and instal them

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and these are the versions of those libraries.

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Notice the two equal signs in here is just the syntax used

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in requirements.txt files to signal

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what version of the library we're using.

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We've also got a .env file with a new instance URL

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and that's just something I've just created in ElephantSQL.

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You can create one and put it in there as well

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and .env.example with a database you arrive in.

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Then, we get to the meat of it.

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We've got app.py and database.py.

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Let's first talk about database.py.

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We've got three tables in this project:

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polls, options, and votes.

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I'm just gonna close the left-hand side

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so that we get a better view of this code.

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In the polls table, we have three columns.

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The id, which is a serial primary key,

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the title, which is text, and the owner,

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or the user that created this poll.

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Know that this owner is not a foreign key

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to some user's table, it's just a string there

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for us to identify who created the poll.

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It's not unique or anything like that.

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The options table has again three columns:

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the id, which is another primary key, serial as well,

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the option text or what people are going

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to be voting for, and the poll id.

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This is a foreign key onto the polls table.

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So, these two are related through that.

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Finally, we've got the votes table, which has

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the user name of the person who voted,

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as well as the option that they voted for.

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We don't need the poll id here because options have

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a unique id and they are related to polls,

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so we can find out the poll by going through options.

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The FOREIGN_KEY here is option_id and it references

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the options table id column.

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We've got a couple of queries in here to select all

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the polls and to select poll with options by using a join.

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That just gives us the poll information as well as each

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of the options in the table, given a poll id.

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And to insert a new option and to insert a new vote.

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So we've got a bunch of things missing here,

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like to insert polls and stuff like that,

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but we're gonna be adding those as we go along.

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Then for these queries we've got our functions.

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Nothing new here as well, they each take a connection,

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create a cursor, and then run the appropriate queries,

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like to create the different tables, to select polls

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and then there's cursor.fetchall.

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Here get_latest_poll is something we're gonna use

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to get the latest poll that was added to the database.

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This, I've put pass in here,

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because we haven't implemented yet.

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We're gonna use some new knowledge in order to do that

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so this is, at the moment, unimplemented.

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Getting poll details, we need a poll id,

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and then we're just gonna SELECT_POLL_WITH_OPTIONS,

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that just gives us essentially everything about a poll

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and then we return cursor.fetchall.

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To get a poll and the vote results that includes

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the vote percentage associated with it,

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we've got pass in there at the moment,

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we're gonna be implementing there later on.

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To get a random poll vote which would give us

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essentially the winner on a poll, we've got pass as well,

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we're gonna be implementing that later on.

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Creating a poll because it takes in the title

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and the owner as well as the options,

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we're gonna be implementing this later on as well.

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And finally to add a poll vote, that's just

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the INSERT_VOTE there, so we've got that running there.

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All right, so not much new in database.py,

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but again, that was of course the point of this,

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not to give you anything too new.

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Now we're gonna go over to app.py

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and I'll show you what we've got in here,

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which is quite a bit, so please bear with me.

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The imports, you may get an error here saying

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DivisionByZero is not a class inside psycopg2.errors.

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What I've done is I've just ignored that

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so on here you can essentially click ignore

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if you do get that error.

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If you're using VS code or anything

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like that that's not PyCharm,

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you're not gonna get an error, that's fine.

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This works, it's just due to how psychopg2 is built

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that it gives an error in PyCharm.

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Then we've got our constant database prompt

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asking the user for the database URI.

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The menu prompt to show him the different options

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in the menu and the new option prompt when we have

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to add new options into a poll,

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that just tells the user what to do.

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So, to create a poll, we're going to ask the user

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for a title and the owner of the poll,

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then we're gonna create an empty options list,

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and then we're gonna use this walrus operator

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that we've looked at before to keep adding new options

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to this list as strings until they enter an empty string,

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and then we're gonna pass all of that to create poll.

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So at the moment, this is not implemented, the create_poll,

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so we're gonna look at that later on.

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To list the open polls, we're just gonna do

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database.get_polls and then we're gonna destruction in here,

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the different poll fields, and we're gonna print them out.

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Prompting for a vote, we're gonna ask for the poll id

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that the user wants to vote on,

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we're gonna get its details, we're gonna print

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the different options out, and then we're gonna ask them

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for which option they want to vote for as well as

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what their username is and we're gonna pass

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all of that data to add_poll_vote.

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Printing the polls options just goes through them

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and prints their details out.

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We're gonna look into more detail

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as to how this works in just a moment.

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And then show_poll_votes is gonna essentially ask the user

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for the poll that they wanna see votes for,

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then it's gonna get the count and percentage

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of votes for each option in a poll

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using database.get_poll_and_vote_results.

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We haven't implemented this yet, but we will do.

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And this can raise DivisionByZero error,

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if there are no votes, because it'll try to divide by zero

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which it can't do so then we're gonna print no votes yet.

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Otherwise, if we didn't get an error,

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that means this ran successfully,

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then we jump into here and we're gonna print that stuff out.

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Notice that we're using .2f here

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as the formatting guide specifies.

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You can use for printing to two decimal places.

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I'm gonna leave a link in the resources section

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of this video in case you don't know what that is.

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All right so this is the more complicated thing so far,

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but we're going to analyse it in more detail

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as we implement get_poll_and_vote_results.

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Finally, randomize_poll_winner takes in a poll id,

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prints out the poll options, and then asks for the option id

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that is the winner, and then goes into the database

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and gets a random vote out of this option,

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and then it's gonna print it out.

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We're gonna use the database to get the random vote,

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so we're gonna learn how to do that later on.

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Finally, we have here the MENU_OPTIONS,

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so if the user types one,

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we're gonna run prompt_create_poll.

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If they type two, we're gonna run

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list_open_polls and so forth.

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But as you can see, this dictionary here

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is a mapping of strings, like one, two, and three,

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to functions, prompt_create_poll, for example.

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It does not run the function.

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You would have to run the function

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with the brackets like that.

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So we're not doing that here,

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we're simply mapping the strings

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to the functions themselves.

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Why?

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Because later on in the menu down here,

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what we're gonna do is we're going to access

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the selection that the user typed, for example, two,

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and we're gonna run that.

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So this is a little bit of syntax here

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that simplifies our menu greatly.

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Let's go through this menu function, by the way.

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First of all, we're asking for the database URI

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using the DATABASE_PROMPT which tells the user

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that they can leave it empty if they want

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to load from the .env file.

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So if they don't type anything, we'll load

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from the .env and then we set that

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from the environment variables, then we create

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the connection to the database, and we use that

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to create the tables, then again with the walrus operator,

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we allow the user to select an option.

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This will be the string one, two, three, four, or five.

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Then we go into the menu options and select

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the appropriate function using that string.

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For example let's say they entered three,

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then this piece of text that's highlighted

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would return prompt_vote_poll,

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so that would essentially replace that,

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and as you can see this is how we run the function.

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We grab the function from there and then we run it,

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passing the connection to it, so that it can use it inside.

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Otherwise if they entered something that is not one

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of these things, that would give us a KeyError,

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in which case we print that an invalid input

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was selected and please try again.

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At the very end, we run the menu function as well.

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So I know this is a lot to take in.

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I would really recommend you download this code,

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go through it slowly, try to understand it fully.

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I just wanted to save you some time,

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not have to write all of this stuff

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that we've already written before in front of you.

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So please do download it and check it out

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and once you're ready, we can continue with the next video.

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All right, so once you're happy with that,

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join me in the next video.

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Thank you for watching and I'll see you in the next one.