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Welcome back.

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Let's get started with flasks.

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By going through a very simple Hello World site example we're going create our first website flask and

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this is essentially the simplest site possible with a flask web framework.

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We're simply going to just return a single string Hello puppy onto a web page just in case you have

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installed the app.

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Make sure you've either done Condon's flask or pitmen small flask at your command line.

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Let's go through the code and then we'll jump to the text editor and actually write it out ourselves.

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Here we see the code that we're going to be using to create our simple web page.

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Let's go line by line and discuss the details of all this and then we'll head over to the text editor

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and type it out.

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So first off for saying from that flask package import the flask class.

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So notice here the capitalization is very easy to make a typo there.

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That flask class has upper case f the package itself is lowercase f.

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Then we have this line.

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We're saying app is equal to flask.

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And we're passing an underscore underscore name underscore underscore.

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Essentially what this line is doing is it's creating an application object over on the left hand side

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as an instance of the class flask imported from the Flast package from the first line and the name variable

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that's being passed into that flask class call.

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That's a python pre-define a variable.

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As we've previously talked about which is then set to the name of the module in which it is used essentially

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answering the question Are we running this script that correctly and flask is able to use the location

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of the module that we pass in as a starting point when it needs to load other resources or other files.

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Those are things such as template files which were going to be discussing later on.

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So once you've created that application where we can do is add pages to it and in this case let's jump

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over past that route function or route decorator and go down here to where we see Death Index return.

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Hello puppy.

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What this function is doing is defining a page index with the function and then it's going to return

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the string later on we're going to return the ability to actually render an entire template of HTML

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code.

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But it's that all we're doing right now is just returning a single string and it actually has h tim

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l code in it.

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It's saying hello Papy as a header one which means when we actually call that index page we're going

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to return that string.

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The browser is going to read that in as h HTML code and we should see help Papy in strong large bold

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text.

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Now the decorator above that function directly links that page to whatever route on your web application.

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It should be at for instance right now we're just saying a single forward slash which is essentially

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the same thing as your home page or your domain.

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So if you're launching this site at WW I love puppies dot com then if you went to AILA politico.com

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that single home page you would see.

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Hello puppy.

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Later on we're going to show you how you can add multiple pages through routing.

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But right now all this is saying is with our application route to this your L and in this case since

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it's a single slash.

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This is your home page and then return back that function which is the index page and it returns back.

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Hello puppy.

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At the very end we have this line which as we've already discussed in the Python section where we say

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if name is equal to main essentially if you're running the script then run your application and later

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on also see how he can set debug equal to true inside of this run call.

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So we can debug our application in real time if we're ever actually serving this to the Web and other

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people are going to be using it.

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You want to make sure you set debug equal to false which is the default.

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So that's all the code.

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Let's go ahead and go back to our text editor and type this out and see if it works.

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Lori here I am at my desktop.

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I'm have a flask underscore examples folder and underneath the folder I'm going to create a new file.

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And I'm just going to call it basic dot PI.

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You can technically call it whatever you want just do not call it flasks that pi.

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Otherwise Python's going to confuse.

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When you try to import things from flask.

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So call it essentially anything you want that's not flasks of Pi.

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OK so basic that pie.

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And what I want to do now is say from flask import flask that I will create my flask application by

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saying grab an instance of this flask class and then pass in my predefined name variable then when I'm

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going to do is grab my application and I'm going to set a route.

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And the first route is just going to be to the home page or the domain name.

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So I just have a single forward slash later on I'll be more clear what this line is doing when we actually

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link it to other pages in our application.

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But right now this is just a single page application and below this we're going to have the function

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that defines what is actually shown.

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When you go to that specific route on your application in this case the home page and we're going to

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return the string to the browser that says Hello puppy or whatever we want.

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And it's going to be a better one.

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And then finally here at the bottom we're going to say if name is equal to Main take my application

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and run it I'm going to say this and let's run now this python script at our command line will call

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Python basic thought pie.

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And when you run this expand this just a little bit you should notice now it says running at HTP 1 2

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7 0 0 0 1 5000.

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If you're running multiple flask examples for instance you have multiple tabs open.

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You may see this last four digit number change a little bit.

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We're going to do is we're going to highlight this and copy it.

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Be careful not to use Control-C copy because that actually quits the server and let's type this or paste

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this into our browser and check it out.

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I'm going to drag over my browser now.

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Here it is.

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And it says hello puppy.

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So you can zoom in here and check out.

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Hello puppy.

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You should see it as a header one.

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And if I right click and say view page source I get to see the actual source that I returned back H-1.

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Hello puppy.

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And as I mentioned later on we're actually going to pasan for HTML files to our flask application.

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But notice here it's just at the home page of this local Your L or IP address we have.

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Hello puppy.

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All right.

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That's the very basics.

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You've now successfully ran your first flask application.

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Not so bad.

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Later on we're going to see how we can expand off of this to have multiple pages sync up if a database

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have interactivity with users and so on.

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But with just 10 lines of code and you already have a full application working great We'll see you in

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the next lecture.