This appendix describes the installation of the Google App Engine Software Development Kit (SDK) on a Macintosh and running a simple “Hello, world” application.
The App Engine SDK allows you to run Google App Engine Applications on your local computer. It simulates the runtime environment of the Google App Engine infrastructure.
This excerpt is from Using Google App Engine. With this book, you can build exciting, scalable web applications quickly and confidently, using Google App Engine -- even if you have little or no experience in programming or web development. Using Google App Engine provides an overview of the tools necessary to use Google App Engine, including Python, HTML, Cascading Style Sheets (CSS), and HTTP. You'll also learn what's required to deploy your applications to Google servers.
Download the appropriate install package for the Google App Engine SDK from http://code.google.com/appengine/downloads.html, as shown in Figure C.1, “Downloading Google Application Engine”.
Download the Mac OS X installer. It should automatically mount as a virtual drive (Figure C.2, “The App Engine Installer”).
Drag the GoogleAppEngineLauncher to the
Applications folder on your hard drive. This
step copies Google App Engine and installs it as an application on your
system. Once this is done, you can eject the virtual drive.
Navigate to the
folder on your main disk, find the AppEngineLauncher icon, and launch
it. You may need to scroll to the bottom of your screen to see the App
Click Accept or Open in any dialog box that asks whether it is OK to launch, as shown in Figure C.3, “Installing Google App Engine”.
When the Engine launches for the first time, it asks if you want to make Command Symlinks, as shown in Figure C.4, “Making symbolic links”.
Click OK. This step will allow you to run App Engine from the command line later. You will have to type an administrator password to make the links.
At this point, you can actually close the App Engine Launcher—you will run the application from the command-line interface (the Terminal application) instead of using the Launcher user interface.
Make a folder for your Google App Engine applications. I am going
to name the folder on my Macintosh Desktop
apps. The path to this folder is:
/Users/csev/Desktop/apps—obviously your path will
use your account name instead of mine. Then make a subfolder in within
Create a file called
ae-01-trivial folder with
the following contents:
application: ae-01-trivial version: 1 runtime: python api_version: 1 handlers: - url: /.* script: index.py
If you are looking at a PDF copy of this book, please do not copy and paste these lines into your text editor. You might end up with strange characters. Just type them into your editor.
Then create a file in the
ae-01-trivial folder called
index.py, with three lines of Python:
print 'Content-Type: text/plain' print '' print 'Hello there Chuck'
Then start the Terminal program, which can be found under
Applications→Utilities→ Terminal. Use the
cd command to navigate to the
apps directory, as shown in Figure C.5, “Navigating to the apps directory”.
When you are in the
directory, start the Google App Engine Web Server and run your
application using the following command:
You will be asked if you want App Engine to check for updates
y); after a few messages, the
server will start up, as shown in Figure C.6, “Starting the application server”.
The last line tells you which port your application is running on and what URL you should use to access your application; in this case, our application is at http://localhost:8080.
Paste http://localhost:8080 into your browser and you should see your application, as shown in Figure C.7, “Your Google application”.
Just for fun, edit the
index.py to change the name “Chuck” to your
own name and refresh the page in the browser to verify your
With two files to edit, there are two general categories
of errors that you may encounter. The first common error is making a
mistake in your
app.yaml file. If
you make a mistake on the
file, App Engine will not start, and you will see an error as shown in
Figure C.8, “Error in app.yaml”.
In this instance, the mistake is an incorrectly indented final
line in the
When you make a mistake in the
app.yaml file, you must the fix the mistake
and attempt to start the application again.
The second type of error is in the
index.py file. If you make a syntax error in
index.py file, the error will
appear in your browser. The error looks terrible and looks like
everything went wrong, as shown in Figure C.9, “Syntax error”.
Do not be alarmed! Ignore most of the output and scroll to the
very bottom of the error output. The error you need to see is likely to
be the very last line of the output—in this case, I made a Python syntax
error on the first and only line of our one-line
index.py file, as shown in Figure C.10, “Finding the syntax error”.
See also http://en.wikipedia.org/wiki/Stack_trace for more information.
If you make a mistake in a file like
index.py, you can just fix the file and
refresh your browser—there is no need to restart the server.
To shut down the server, go into the window where you
started the server and press Ctrl-C to abort the server. You should see
a message that says something like “Server interrupted by user,
terminating” and the server will shut down. You can start it back up
again. When the server is shut down, navigating to
http://localhost:8080 will fail because there is no
software running on and listening to port 8080.
If you enjoyed this excerpt, buy a copy of Using Google App Engine.
Copyright © 2009 O'Reilly Media, Inc.