Using the Users Service

To personalize your application's greeting using the Users service, edit your helloworld/main.py file as follows:

import webapp2

from google.appengine.api import users

class MainPage(webapp2.RequestHandler):
  def get(self):
    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))

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

Launch the application using the dev_appserver and reload its page (such as http://localhost:8080 ) in your browser. You'll be redirected to the local version of the Google sign-in page suitable for testing your application. You can enter any user name you'd like, and your application will see a fake User object based on that user name.

When your application is running on App Engine, users will be directed to the Google Accounts sign-in page, then redirected back to your application after successfully signing in or creating an account.

The Users API

Let's take a closer look at the new pieces:

user = users.get_current_user()

If the user is already signed in to your application, get_current_user() returns the User object for the user; otherwise, it returns None .

if user:
  self.response.headers['Content-Type'] = 'text/plain'
  self.response.out.write('Hello, ' + user.nickname())

If the user has signed in, display a personalized message, using the nickname associated with the user's account.

else:
  self.redirect(users.create_login_url(self.request.uri))

If the user has not signed in, tell webapp2 to redirect the user's browser to the Google Accounts sign-in screen. The redirect includes the URL back to this page ( self.request.uri ), so the Google Accounts sign-in mechanism will send the user back here after signing in or registering for a new account.

For more information, see the Users API documentation .

Summary and Review

Your application can now greet visiting users by name. Launch the application locally and try logging in and out.

In the next lesson , we'll add a feature to let users greet each other by using a form to submit guestbook messages.