Python for Decision Makers and Business Leaders Transcripts
Chapter: Web development with Python
Lecture: Hello world Flask
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Here we are in our Python IDE, called PyCharm.
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There's a couple of good editors out there in the world.
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PyCharm is one of them, my favorite.
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There's also a Visual Studio Code
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and a couple of other options.
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I've already set up a project
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by just creating a couple of folders and a file here.
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To say that, we're going to use Flask.
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And we're going to start by creating
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the Hello World Flask application and then we're going to
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extend that out, quite a bit.
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Often, people think the Hello World app idea is to show you
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the simplest thing that you could possibly do to get
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Hello World on the screen.
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But actually one of the important things of these, Hello
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World little demo applications is to show you the entire
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system is, kind of, hanging together and working.
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Yes, I can run Python.
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Yes, I can open up the web server and things like that.
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So, let's do that, real quick here.
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Want a new Python file, my convention
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is typically called app, and in order to use a
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library in Python regardless of whether it is one of these
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built-in standard library ones
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these batteries included or an external one
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that I have gotten installed
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you just type import and the name of it.
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Here, you can see it automatically helps us out.
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It says Flask, that's what we want to use.
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So in here when I create a thing called app
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and we say Flask dot capital Flask
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and we give it the name of this file
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which you can get to like that.
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Now we have to create a function which is called
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when somebody requests a webpage.
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So I'll just call that index or something like that.
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And here we're just going to say something like
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really simple return Hello world like that.
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How about Hello Flask.
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Now this itself is not enough to reformat that
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This itself is not enough to make it exposed to Flask.
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We've got to do one more thing.
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We're going to go over here and say app this is a route
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as in a destination URL, it's just forward slash.
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Then finally down here we're going to say app.run.
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Now there's a little convention in Python
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that allows us to import this into
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a production server or run it in testing.
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So I'm going to do that here like this.
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We'll go ahead and tell it it's in it's debug mode.
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So in order to run it I just right click and say run.
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There's our web server.
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Look at that, it's already off to a good start.
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What happens if I click on it?
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Well, Hello Flask.
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Whoo, make that nice and big, there we go
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way more dramatic when it's huge right?
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Hello Flask, that's it.
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So we've created our Flask web application.
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There was no compile step, there was no installing
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things other than to get this installed into here.
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Which I did before.
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But there's no like messing with the system
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and things like that, it's just write these couple of lines
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run it, and we're off to the races with our Flask web app.