1.. _tutorials.gettingstarted.usingusers: 2 3Using the Users Service 4======================= 5Google App Engine provides several useful services based on Google 6infrastructure, accessible by applications using libraries included with the 7SDK. One such service is the Users service, which lets your application 8integrate with Google user accounts. With the Users service, your users can 9use the Google accounts they already have to sign in to your application. 10Let's use the Users service to personalize this application's greeting. 11 12 13Using Users 14----------- 15Edit ``helloworld/helloworld.py`` again, and replace its contents with the 16following:: 17 18 from google.appengine.api import users 19 import webapp2 20 21 class MainPage(webapp2.RequestHandler): 22 def get(self): 23 user = users.get_current_user() 24 25 if user: 26 self.response.headers['Content-Type'] = 'text/plain' 27 self.response.out.write('Hello, ' + user.nickname()) 28 else: 29 self.redirect(users.create_login_url(self.request.uri)) 30 31 application = webapp2.WSGIApplication([ 32 ('/', MainPage) 33 ], debug=True) 34 35 def main(): 36 application.run() 37 38 if __name__ == "__main__": 39 main() 40 41Reload the page in your browser. Your application redirects you to the local 42version of the Google sign-in page suitable for testing your application. 43You can enter any username you'd like in this screen, and your application 44will see a fake ``User`` object based on that username. 45 46When your application is running on App Engine, users will be directed to the 47Google Accounts sign-in page, then redirected back to your application after 48successfully signing in or creating an account. 49 50 51The Users API 52------------- 53Let's take a closer look at the new pieces. 54 55If the user is already signed in to your application, ``get_current_user()`` 56returns the ``User`` object for the user. Otherwise, it returns ``None``:: 57 58 user = users.get_current_user() 59 60If the user has signed in, display a personalized message, using the nickname 61associated with the user's account:: 62 63 if user: 64 self.response.headers['Content-Type'] = 'text/plain' 65 self.response.out.write('Hello, ' + user.nickname()) 66 67If the user has not signed in, tell ``webapp2`` to redirect the user's browser 68to the Google account sign-in screen. The redirect includes the URL to this 69page (``self.request.uri``) so the Google account sign-in mechanism will send 70the user back here after the user has signed in or registered for a new 71account:: 72 73 self.redirect(users.create_login_url(self.request.uri)) 74 75For more information about the Users API, see the `Users reference <http://code.google.com/appengine/docs/python/users/>`_. 76 77 78Next... 79------- 80Our application can now greet visiting users by name. Let's add a feature that 81will let users greet each other. 82 83Continue to :ref:`tutorials.gettingstarted.handlingforms`. 84