Cloud computing lectures: Programming with Google App Engine Keke Chen

Outline Using google app engine - walk through a simple example

Background: how cgi works Request : content/url sent by the client Response: content return to the client’s browser 3 Client server Request: request a url, click a button, etc Request a url: “get” url Response: CGI returns some html code Click buttons: “post” something

Python “hello world” CGI program helloworld.py print 'Content-Type: text/plain' print '' print 'Hello, world!'

Preparation Have your gmail account Installing google apps tool – dev_appserver.py, the development web server dev_appserver.py – appcfg.py, for uploading your app to App Engine appcfg.py

Setup the development env Windows/mac: check s.html to find the package s.html Nimbus17: already installed at /usr/local/gae

Webapp does Wraps the CGI functions – API for handling request/response Python Web Server Gateway Interface (WSGI) – A framework for developing CGI programs with Python 7

from google.appengine.ext import webapp from google.appengine.ext.webapp.util import run_wsgi_app class MainPage(webapp.RequestHandler): def get(self): self.response.headers['Content-Type'] = 'text/plain' self.response.out.write('Hello, webapp World!') application = webapp.WSGIApplication( [('/', MainPage)], debug=True) def main(): run_wsgi_app(application) if __name__ == "__main__": main()

Configuration file app.yaml – A standard file format for configuration – A set of API designed to access the configuration – – Don’t need to know much about yaml – Check GAE’s typical configurations 9

App.yaml application: helloworld version: 1 runtime: python27 threadsafe: false api_version: 1 handlers: - url: /.* script: helloworld.py If threadsafe is set to true, use helloworld.application

Start development server How to start /usr/local/gae/dev_appserver.py helloworld/ -p port -a address

Use users service Use the google account service 12

Using users service user = users.get_current_user() if user: self.response.headers['Content-Type'] = 'text/plain' self.response.out.write('Hello, ' + user.nickname()) else: self.redirect(users.create_login_url(self.request.uri))

Handling forms with webapp self.response.out.write(""" """)

db - datastore db.Model GQL: sql like query language greetings = db.GqlQuery("SELECT * FROM Greeting ORDER BY date DESC LIMIT 10") Or omit select *: greetings = Greeting.gql("ORDER BY date DESC LIMIT 10") With parameters: greetings = Greeting.gql("WHERE author = :1 ORDER BY date DESC",users.get_current_user()) greetings = Greeting.all() greetings.filter("author =", users.get_current_user()) greetings.order("-date") 16

Entity group Passing parameters

Use templates Templates are used to generate the similar webpages with different variables 19

Use stylesheet Change app.yaml Include the code for using stylesheet

Upload application Create an application at Google AppEngine Change the app name in app.yaml correspondingly Run appcfg.py update helloworld/