Why does manage.py syncdb fail to connect to google cloud sql database?

During a recent update of an app on Google App Engine I was in the process of updating the database with:

SETTINGS_MODE='prod' ./manage.py syncdb

This worked last time I ran it, but now I am getting the following error:

Traceback (most recent call last):
  File "./manage.py", line 10, in <module>
    execute_from_command_line(sys.argv)
  File "/Library/Python/2.7/site-packages/django/core/management/__init__.py", line 399, in execute_from_command_line
    utility.execute()
  File "/Library/Python/2.7/site-packages/django/core/management/__init__.py", line 392, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/Library/Python/2.7/site-packages/django/core/management/base.py", line 242, in run_from_argv
    self.execute(*args, **options.__dict__)
  File "/Library/Python/2.7/site-packages/django/core/management/base.py", line 285, in execute
    output = self.handle(*args, **options)
  File "/Library/Python/2.7/site-packages/django/core/management/base.py", line 415, in handle
    return self.handle_noargs(**options)
  File "/c/clients/green_rentals/code/green-rental/south/management/commands/syncdb.py", line 92, in handle_noargs
    syncdb.Command().execute(**options)
  File "/Library/Python/2.7/site-packages/django/core/management/base.py", line 285, in execute
    output = self.handle(*args, **options)
  File "/Library/Python/2.7/site-packages/django/core/management/base.py", line 415, in handle
    return self.handle_noargs(**options)
  File "/Library/Python/2.7/site-packages/django/core/management/commands/syncdb.py", line 57, in handle_noargs
    cursor = connection.cursor()
  File "/Library/Python/2.7/site-packages/django/db/backends/__init__.py", line 159, in cursor
    cursor = util.CursorWrapper(self._cursor(), self)
  File "/c/downloads/python/google_appengine/google/storage/speckle/python/django/backend/base.py", line 263, in _cursor
    if not self._valid_connection():
  File "/c/downloads/python/google_appengine/google/storage/speckle/python/django/backend/base.py", line 258, in _valid_connection
    return super(DatabaseWrapper, self)._valid_connection()
AttributeError: 'super' object has no attribute '_valid_connection'

I tried updating the Google App Engine SDK to the latest (1.8.8) and I also tried re-authenticating with oauth (that worked). Still getting the same message though. Any clues as to why?

Thanks in advance!

Edit:

It looks like the settings I was using for the database connection have changed recently. I used to use:

DATABASES = {
    'default': {
        'ENGINE': 'google.appengine.ext.django.backends.rdbms',
        'INSTANCE': 'project-id:instance-id',
        'NAME': 'name',
    }
}

But now the recommendation is:

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.mysql',
        'HOST': '/cloudsql/your-project-id:your-instance-name',
        'NAME': 'database-name',
        'USER': 'mysql-user',
    }
}

After updating to that, I now get a new error:

Traceback (most recent call last):
  File "./manage.py", line 10, in <module>
    execute_from_command_line(sys.argv)
  File "/Library/Python/2.7/site-packages/django/core/management/__init__.py", line 399, in execute_from_command_line
    utility.execute()
  File "/Library/Python/2.7/site-packages/django/core/management/__init__.py", line 392, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/Library/Python/2.7/site-packages/django/core/management/base.py", line 242, in run_from_argv
    self.execute(*args, **options.__dict__)
  File "/Library/Python/2.7/site-packages/django/core/management/base.py", line 285, in execute
    output = self.handle(*args, **options)
  File "/Library/Python/2.7/site-packages/django/core/management/base.py", line 415, in handle
    return self.handle_noargs(**options)
  File "/c/clients/green_rentals/code/green-rental/south/management/commands/syncdb.py", line 89, in handle_noargs
    db.connection_init() 
  File "/c/clients/green_rentals/code/green-rental/south/db/mysql.py", line 180, in connection_init
    cursor = self._get_connection().cursor()
  File "/Library/Python/2.7/site-packages/django/db/backends/__init__.py", line 159, in cursor
    cursor = util.CursorWrapper(self._cursor(), self)
  File "/Library/Python/2.7/site-packages/django/db/backends/__init__.py", line 129, in _cursor
    self.ensure_connection()
  File "/Library/Python/2.7/site-packages/django/db/backends/__init__.py", line 124, in ensure_connection
    self.connect()
  File "/Library/Python/2.7/site-packages/django/db/utils.py", line 99, in __exit__
    six.reraise(dj_exc_type, dj_exc_value, traceback)
  File "/Library/Python/2.7/site-packages/django/db/backends/__init__.py", line 124, in ensure_connection
    self.connect()
  File "/Library/Python/2.7/site-packages/django/db/backends/__init__.py", line 112, in connect
    self.connection = self.get_new_connection(conn_params)
  File "/Library/Python/2.7/site-packages/django/db/backends/mysql/base.py", line 435, in get_new_connection
    conn = Database.connect(**conn_params)
  File "/Library/Python/2.7/site-packages/MySQLdb/__init__.py", line 81, in Connect
    return Connection(*args, **kwargs)
  File "/Library/Python/2.7/site-packages/MySQLdb/connections.py", line 187, in __init__
    super(Connection, self).__init__(*args, **kwargs2)
django.db.utils.OperationalError: (2002, "Can't connect to local MySQL server through socket '/cloudsql/your-project-id:your-instance-name' (2)")

(Where your-project-id:your-instance-name have been changed appropriately).