Gate

Hello World

Just the barebones

Got all that? I didn't think so. If all you took away from that is "Mitochondria is the powerhouse of the cell", I think you'll still be okay. That's probably my fault, though. I just threw five pages of gobbly gook text at you without any actual examples. I've hoped you've been following along in the terminal, but I know that's optimistic. So far, everything I've been covering has just been the basics for the technologies and languages that I'll be using; things that you should probably be learning from other, more complete tutorials. And all of the example checkpoints that I wrote (available on my GitHub) haven't actually been useful... until now! Bum bum buuummm.

To get the code in all of the Checkpoints download a zip file of the project, and then unzip it.

Goal

We will now actually begin to put all of the pieces together. By the end of this page you should be caught up to Checkpoint 1 - Barebone.

Let the Games Begin

Make sure that you have the Google App Engine SDK downloaded and installed. If you don't, go here to do it.

Open Terminal and navigate to a directory where you'll want to keep all of your work. I will be working out of a directory called "gate" in "~/Desktop/projects". All we'll need to get started are two files: app.yaml, and barebone.py.

app.yaml


version: 1
runtime: python27
api_version: 1
threadsafe: true

handlers:
- url: /.*
  script: barebone.app

This file is just some configuration settings that are required by Google App Engine to understand how it is supposed to handle your webapp. The important things to notice are line 2 and lines 6 - 8. Line 2 says that the app will be using version 2.7 of Python. Lines 6 - 8 says that the barebone application will handle all web requests.

barebone.py


import webapp2

class MainPage(webapp2.RequestHandler):
  def get(self):
    self.response.write("Hello, World!")

class SecondPage(webapp2.RequestHandler):
  def get(self):
    self.response.write("New page!")

app = webapp2.WSGIApplication([
  ('/', MainPage),
  ('/two', SecondPage),
], debug=True)

This is where the interesting stuff happens. Let's start at the beginning.

There is a webapp2 library that the Google App Engine SDK provides. When you import it, you become able to use things like the RequestHandler and the WSGIApplication. These things take care of a lot of little details you shouldn't worry about.

With this webapp2 library, each web page you create can be thought of as a Python class. Each class will have a function called get so that you can request the webpage. In this example, when the MainPage webpage is requested, "Hello, World!" will be returned and displayed on the page, and SecondPage will display "New page!". If you're paying close attention you'll notice that this isn't using any HTML, even though that's all we covered in the last section. But don't worry, we'll start using some HTML soon.

The last four lines of barebones.py are routing requests to the correct handlers. When a request is made for '/' (this represents the root of your application), it will be handled by the MainPage class. When someone requests 'whatever.com/two', the SecondPage class will handle that request.

Time to Test

If you downloaded and installed the Google App Engine SDK correctly, and installed it to /usr/local/, you just have to execute one command to get your Hello World example running.

cd out of your working directory, and start your dev server.


cd ..
/usr/local/google_appengine/dev_appserver.py gate

Now go to "localhost:8080" in your web browser and you will see "Hello, World!". It's not very impressive at this point, but it's a huge milestone. Pat yourself on the back and go eat some girl scout cookies to celebrate.

Gate Home GitHub