Google App Engine

User Objects

An instance of the User class represents a user. User instances are unique and comparable. If two instances are equal, then they represent the same user.

The application can access the User instance for the current user by calling the users.get_current_user() function.

from google.appengine.api import users

user = users.get_current_user()
if not user:
    # The user is not signed in.
else:
    print "Hello, %s!" % user.nickname()

You can use the users.get_current_user() function no matter which authentication option your app uses.

A User instance can be also constructed from an email address:

user = users.User("Albert.Johnson@example.com")

Or, if you have a federated_identity, you can use it to create a User instance:

user = users.User(federated_identity="http://example.com/id/ajohnson")

If the User constructor is called with an email address that does not correspond with a valid Google account, the object will be created but it will not correspond with a real Google account. This will be the case even if someone creates a Google account with the given email address after the object is stored. A User value with an email address that does not represent a Google account at the time it is created will never match a User value that represents a real user.

When running under the development web server, all User objects are assumed to represent valid Google accounts when stored in the (simulated) datastore.

The User object for a valid user can provide a unique ID value for the user that stays the same even if the user changes her email address. The user_id() method returns this ID, a str value.

The User object has the same form no matter which method of authentication your app uses. If you switch authentication options from Google Accounts to OpenID, existing User objects in the datastore are still valid. (Note that the support for OpenID is experimental.)

Using User Values With the Datastore

The user ID is stable; you can use it in a key name or as a string property. Therefore, when using user values, you want to store the user ID (and perhaps the last-seen mail address to communicate with the user by mail). The example below shows how to compare the current user to a user ID:

from google.appengine.api import users
from google.appengine.ext import ndb

class UserPrefs(ndb.Model):
    userid = ndb.StringProperty()

user = users.get_current_user()
if user:
    q = ndb.gqlQuery("SELECT * FROM UserPrefs WHERE userid = :1", user.user_id())
    userprefs = q.get()

You probably don't want to store a UserProperty, since it is equal to the email address plus the user's unique ID. If a user changes their email address and you compare their old, stored User to the new User value, they won't match.

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