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Hello, and in this lecture, you will

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build your first website with Flask, if

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you haven't done so already, and Flask

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is a Python framework that has all the

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tools and the templates and the

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functions for you to build the websites with

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Python, and before going deeper into

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Flask and explaining you how to use

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Flask probably for building Python web

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apps, I would like you to spend 3

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minutes to build a very basic website

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with Flask. And that is done with only

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seven lines of Python code. So that's

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what we'll do right now. To build a web

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app with Flask, you need to have Flask

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installed. So

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[No audio]

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pip install flask should

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install Flask in your Python environment.

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[No audio]

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Alright, that was successfully installed.

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And let's create our website now. What you need is a

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Python file. So I'm creating one here,

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let's say script1.py, and then

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here is where you write the code that

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will build your web app, and everything

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starts from importing Flask, and

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actually, you don't import the Flask

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framework, but you import the Flask

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class from a Flask framework. So from

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flask import Flask, and Flask is a

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class of this library. And this contains

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all the prototypes that you need to

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build web apps with Python. So this will

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handle the requests for you. You don't

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have to set up requests yourself. But

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let's focus on this example for now.

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Once you do that, you need to create a

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variable where you will store your Flask

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object instance, your Flask application,

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that will be equal to the Flask

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class, and you pass the name variable in

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there, just don't worry about that right

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now. Then you need a decorator, route,

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and here is the URL where you view your

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website. So this '/' here means the

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homepage and just after that, you need

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to write the function, the Python

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function, and this function is what

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defines what your webpage will do. In

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this case, we will return a string.

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[No audio]

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Let's say a string here, Website content goes

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here. Just after that you need two more

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lines of code, and that's a conditional

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statement, if name equals string main

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[No audio]

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app.run debug equals True. That's

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it. Don't worry about this. Right now,

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just click save, open a Terminal and

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execute your script with python script1 Python, yeah.

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[No audio]

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And it looks like your

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web app is running now. So open the

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browser, and your website should be

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live on your localhost.

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[No audio]

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Now that's it. Nothing impressive, but you see how easy

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is to create a website with Python.

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And in this case, we are just returning

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a string here to the website. So

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that's nothing fancy in there. But later

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on, I'll explain to you how you can

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return HTML pages instead of plain

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Python strings to your website, that will

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allow you to actually have different

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formats, different fonts on your text.

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And then you can also apply CSS styling

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to your HTML, and so you'll have a

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complete website with modern features.

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For now let's make sure you understand

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these seven lines of code. Yep, it's

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seven lines. As I said, the first line

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you are importing the Flask class object

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from the flask library. Then in the next

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line, once you have imported the

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Flask class in here, the Flask object in

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other words, you are instantiating that

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class, that object. And this here is a

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special variable that will get as value of

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the name of the Python script. Now when

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you execute a Python file, a Python

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script, Python assigns the name main, this

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string to the file.

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[No audio]

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When you import a

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script into another script, like if we

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import this script from another script,

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this script will be assigned the script1.py

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name. But when you execute

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the script, Python assigns the name,

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'__main__'.

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So what happens is that, in this

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line, we say if name equals to main,

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then run the app,

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[No audio]

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and this is true

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when we execute the script, as we did

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here. But if we imported the script

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from another script, this line here would

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not be executed. So this allows us to

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have control over this script using this

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line here, then we have these two lines.

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This is a decorator. Now the output that

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this function produces, will be mapped

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to this URL. So if you want, you can

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change this URL to this, for example,

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save the script. Sure, you need a new

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URL here. Save the script, run, and go to

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the localhost, reload, and this time

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you'll get an error, Python couldn't find

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this page. But it can find the about

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page. Yeah, that's it. If you still want an

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homepage, you would add another

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decorator and another function just

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after the decorator.

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So just leave this, the homepage,

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[No audio]

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and just say homepage.

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Here, save. Again, we have an error

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because we cannot have functions with

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the same name. So we can change this to

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about, the name doesn't matter. So this

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doesn't have to be the same with this one,

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click Save, run the script again,

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[No audio]

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and go to the website. This is working.

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Try the homepage, and this is working

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too. If you want to change something,

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let's say About content goes here,

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you save the script,

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and the web app will

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restart by itself. So you don't have to

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close the web app and run the script

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again as I did earlier. If you get an

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error like I got previously, the script

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will stop. But if everything is alright,

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you will not get an error. So

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[No audio]

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try this again. Homepage is fine. The About page is

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fine too, and with the new content. So

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that's about it. In the next lecture,

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you will learn how to return an HTML

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template, an HTML file using your Python

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functions that will give you full power

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to publish anything that you want in

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your website and not just plain strings

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as we did in this lecture. So see you

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in the next lecture.