一段还没琢磨头的django代码

 1 class ModelBackend(object):
 2     """
 3     Authenticates against settings.AUTH_USER_MODEL.
 4     """
 5 
 6     def authenticate(self, request, username=None, password=None, **kwargs):
 7         if username is None:
 8             username = kwargs.get(UserModel.USERNAME_FIELD)
 9         try:
10             user = UserModel._default_manager.get_by_natural_key(username)
11         except UserModel.DoesNotExist:
12             # Run the default password hasher once to reduce the timing
13             # difference between an existing and a non-existing user (#20760).
14             UserModel().set_password(password)
15         else:
16             if user.check_password(password) and self.user_can_authenticate(user):
17                 return user

红色部分大概依稀感觉到是什么意思，没深入研究，有空看看！