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- [Instructor] Hi and
welcome back to the course.

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As we've seen, REST was
designed to be stateless

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and for applications to interact

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with things called resources.

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In this section we're going to be creating

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a proper REST API

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that follows all of the principles.

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In order to do that

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we're also going to
introduce a new library.

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It is an extension to the Flask library

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that we've already used.

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And this extension is going to allow us

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to create REST APIs very easily.

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It is limiting in some sense of the word

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because it decreases the
flexibility of Flask.

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However it does that to make
us adhere to the REST standard

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and that is a good thing
because we will make sure

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that our application follows
what REST was designed to be.

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When other applications such
as mobile apps or web apps

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interact with our API

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it would be easy for the
developers of those applications

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to understand how our API works.

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Flask-RESTful is what we're
going to be installing

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and as I said that's an extension to Flask

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and it just gives us a few goodies

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that we can use in our application.

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In this lecture however
we're going to be setting up

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so apologies for the sort
of a bit more boring content

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this time around

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but we have to do the setup at some point.

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In order to set up for this new project

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I've just gone to a new folder.

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I've called it section4

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and you can see here

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this is the path of
the folder that I am in

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so it's just basically in My Documents

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and what I'm going to do
is I'm going to create

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a virtual environment.

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A virtual environment essentially gives me

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a clean installation of Python.

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Here's pip3.5, remember that?

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We used that to instal
libraries in the last section

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such as Flask.

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If you do pip3.5 freeze

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that is going to give you

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the libraries that you've got installed

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such as Flask

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and the versions that you've
got these libraries on.

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For example right now I've
got Flask version 0.11.1

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and so on with a bunch of other libraries.

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Most of these libraries
are installed by Flask

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when you instal Flask.

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As you can see

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these libraries have
specific version numbers

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and last section we
created our application

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using this version of Flask.

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If we now create another application

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and Flask has been updated,

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for example imagine it
is now in version 0.12,

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we may go into pip3.5 and update
Flask to the latest version

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so we can get any bug
fixes and any new features

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that they've implemented,

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but in doing so

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we may break section 3's application

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if Flask has changed substantially.

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So updating isn't really the best option.

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Instead what we want to do

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is to let the application
in section 3 use 0.11.1

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and we can create our new
project using the newest version.

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In order to do that we have to make sure

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that our projects don't share libraries.

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If we went ahead and just
created a new project

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and ran it using Python 3.5

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that would be using
these libraries up here.

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So what we have to do

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is we have to get a clean
installation of Python

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with no libraries at all

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and use that for this project.

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If we then go ahead and
create a new project later on

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we will also do a fresh
installation of Python again

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and so on and so on.

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However, fortunately we
don't have to download Python

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and reinstall it and so on every time.

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What we want to do is to
use virtual environments.

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A virtual environment
mimics reinstalling Python

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with no libraries.

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The first thing you wanna do

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is do pip3.5 instal virtualenv.

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And then here as you can see

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I've already got this
requirement satisfied

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so it tells me that

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but in your case it will instal virtualenv

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and virtualenv is the tool
that we're going to use

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to create these virtual environments.

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Once that's done

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all we'll do is say virtualenv
venv --python=python3.5.

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Now this is calling the
virtualenv programme

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that we've installed

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and what's going to happen

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is it's going to create a folder
inside our current folder,

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inside this section4 folder that I'm in.

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It's going to create a folder called venv

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and in it it's going to put
a fresh Python installation.

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And that fresh Python instal

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is going to be Python 3.5.

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If you wanted to use Python 2.7

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you may put python2.7 there and so on.

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So just press enter at the end

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and then it will instal a
few things that it needs.

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This is doing the Python instal.

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And there it is, it's now finished.

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The next step is to do,

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sorry, apologies, not activate,

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source venv/bin/activate, there we go.

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Now this will only work
if you're on Mac or Linux.

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If you are on Windows

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what you want to do is
./venv/Scripts/activate.bat.

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This is what you want to
run if you are on Windows

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using the Windows command line.

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Okay?

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But for me I'm going to do
source venv/bin/activate

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and notice how now my
prompt is going to change

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and it's going to show
the bracket venv at first.

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This means that I am now
using the virtual environment.

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Whenever I run Python

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this is going to run Python 3.5

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which is the sort of Python
instal that I've done.

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Notice how in the past
I had to run Python 3.5

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to get this Python version.

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As long as I am within
the virtual environment

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I just have to run
Python to get the version

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that is installed in
the virtual environment.

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Okay so staying in the virtual
environment is very easy

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you just don't have to do anything

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and if you ever want to
leave the virtual environment

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and stop using the virtual environment

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just do deactivate.

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Notice how now if I do python --version

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I go back to the system version

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which is Python 2.7.

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Okay so I'm going to back into
the virtual environment now

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and do pip instal Flask-RESTful.

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Okay so what is going to happen now

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is that I am in the virtual environment

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and I'm going to instal this library

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that is required.

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Notice how installing this
library will also instal Flask

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so you don't have to do that
separately if you don't want

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but you can instal Flask
separately if you prefer

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just by doing pip instal Flask.

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Okay now we can do pip freeze

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and this well tell us
what we've got installed

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and as you can see we've
got a bunch of things

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including Flask, the
same version as before,

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the version hasn't changed yet,

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but it might in the future.

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And we've also got a thing
called Flask-RESTful.

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Now Flask-RESTful is
what's going to allow us

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to very easily create rest APIs.

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So that's us all set up

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and setting up the virtual environment

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and installing Flask-RESTful

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and in the very next video

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we're going to talk about
how to use Flask-RESTful

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to create our API.

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I'll see you there.