Installing and Running Google App Engine on Windows Vista: Appendix B - Using Google App Engine

Download the appropriate Google App Engine SDK install package from http://code.google.com/appengine/downloads.html as shown in Figure B.1, “Downloading Google Application Engine”.

Figure B.1. Downloading Google Application Engine

Download the Windows installer, double-click on the GoogleApplicationEngine installer, and accept any security warning dialog boxes that pop up.

Click through the installation wizard, as shown in Figure B.2, “Installing Google Application Engine”, and it will install App Engine. If you do not have Python 2.5, it will install Python 2.5 as well.

Figure B.2. Installing Google Application Engine

Once the install is complete, you can discard the downloaded installer.

Now you need to create a simple application. Make a folder for your Google App Engine applications. This example installation will be put into a desktop folder called apps: C:\Users\csev\Desktop\apps. Then make a subfolder within apps called ae-01-trivial—the path to this folder is C:\Users\csev\Desktop\apps\ae-01-trivial.

Using a text editor such as jEdit (http://www.jedit.org), create a file called app.yaml in the ae-01-trivial folder with the following contents:

application: ae-01-trivial
version: 1
runtime: python
api_version: 1

handlers:
- url: /.*
  script: index.py

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 Command Prompt program by clicking the Windows icon in the lower-left and typing Command in the Start Search box. When the Command Prompt item is highlighted, press Enter to start the Command Prompt.

Then use the cd command to navigate into the apps directory, as shown in Figure B.3, “Navigating to the application directory”.

Figure B.3. Navigating to the application directory

Start the Google App Engine Web Server and run your application using this command:

"\Program Files\Google\google_appengine\dev_appserver.py" ae-01-trivial

Once App Engine starts with your application, you will be asked if you want App Engine to check for updates (type y) and then, after a few messages, the server will start up, as shown in Figure B.4, “Starting the application server”.

Figure B.4. 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 B.5, “Your Google application”.

Figure B.5. Your Google application

Just for fun, edit index.py to change the name Chuck to your own name and refresh the browser to verify your updates.

With two files to edit, there are two general categories of errors that you may encounter. If you make a mistake in the app.yaml file, App Engine will not start, and you will see an error, as shown in Figure B.6, “Error in app.yaml”.

Figure B.6. Error in app.yaml

In this instance, the mistake was an incorrect indentation in the last line in the app.yaml (line 8).

When you make a mistake in the app.yaml file, you must the fix the mistake and attempt to start the application again.

If you make a syntax error in the index.py file, the error will appear in your browser. The error looks bad, as if everything has gone completely wrong, as shown in Figure B.7, “Syntax error”.

Figure B.7. Syntax error

Do not be alarmed! Ignore most of the output and scroll to the very bottom of the error output. The error that 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 of the first line of our one-line application, as shown in Figure B.8, “Finding the syntax error”.

Figure B.8. 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 close the window to abort the server. When the server is shut down, you will notice that navigating to http://localhost:8080 will fail because there is no software running on and listening to port 8080.