SQLAlchemy with Google Cloud SQL connect to development server - mysql

Question

I am using SQLAlchemy 0.8 with Google App Engine and Cloud SQL. I would like to do a full integration test locally before deploying, but I cannot get SQLAlchemy to connect to my development MySQL server using the mysql+gaerdbms dialect
create_engine(
'mysql+gaerdbms:///test?instance=homingbox:instance1'
)
I start my app engine from the command line as follows
python dev_appserver.py --mysql_user=username --mysql_password=root ../Source/HomingBox/gae
Whenever I try to hit the database I get this lovely stack trace
ERROR 2013-04-22 21:35:39,987 webapp2.py:1528] (ImportError) None None
Traceback (most recent call last):
File "/home/leon/Development/google_appengine/lib/webapp2-2.3/webapp2.py", line 1511, in __call__
rv = self.handle_exception(request, response, e)
File "/home/leon/Development/google_appengine/lib/webapp2-2.3/webapp2.py", line 1505, in __call__
rv = self.router.dispatch(request, response)
File "/home/leon/Development/google_appengine/lib/webapp2-2.3/webapp2.py", line 1253, in default_dispatcher
return route.handler_adapter(request, response)
File "/home/leon/Development/google_appengine/lib/webapp2-2.3/webapp2.py", line 1077, in __call__
return handler.dispatch()
File "/home/leon/Development/google_appengine/lib/webapp2-2.3/webapp2.py", line 547, in dispatch
return self.handle_exception(e, self.app.debug)
File "/home/leon/Development/google_appengine/lib/webapp2-2.3/webapp2.py", line 545, in dispatch
return method(*args, **kwargs)
File "/home/leon/Development/Source/HomingBox/gae/rest.py", line 19, in get_list
self.response.write(json.dumps(application.get_list()))
File "/home/leon/Development/Source/HomingBox/gae/dal.py", line 98, in get_list
return query.all()
File "/home/leon/Development/Source/HomingBox/gae/sqlalchemy/orm/query.py", line 2140, in all
return list(self)
File "/home/leon/Development/Source/HomingBox/gae/sqlalchemy/orm/query.py", line 2252, in __iter__
return self._execute_and_instances(context)
File "/home/leon/Development/Source/HomingBox/gae/sqlalchemy/orm/query.py", line 2265, in _execute_and_instances
close_with_result=True)
File "/home/leon/Development/Source/HomingBox/gae/sqlalchemy/orm/query.py", line 2256, in _connection_from_session
**kw)
File "/home/leon/Development/Source/HomingBox/gae/sqlalchemy/orm/session.py", line 797, in connection
close_with_result=close_with_result)
File "/home/leon/Development/Source/HomingBox/gae/sqlalchemy/orm/session.py", line 801, in _connection_for_bind
return self.transaction._connection_for_bind(engine)
File "/home/leon/Development/Source/HomingBox/gae/sqlalchemy/orm/session.py", line 297, in _connection_for_bind
conn = bind.contextual_connect()
File "/home/leon/Development/Source/HomingBox/gae/sqlalchemy/engine/base.py", line 1669, in contextual_connect
self.pool.connect(),
File "/home/leon/Development/Source/HomingBox/gae/sqlalchemy/pool.py", line 272, in connect
return _ConnectionFairy(self).checkout()
File "/home/leon/Development/Source/HomingBox/gae/sqlalchemy/pool.py", line 425, in __init__
rec = self._connection_record = pool._do_get()
File "/home/leon/Development/Source/HomingBox/gae/sqlalchemy/pool.py", line 855, in _do_get
return self._create_connection()
File "/home/leon/Development/Source/HomingBox/gae/sqlalchemy/pool.py", line 225, in _create_connection
return _ConnectionRecord(self)
File "/home/leon/Development/Source/HomingBox/gae/sqlalchemy/pool.py", line 318, in __init__
self.connection = self.__connect()
File "/home/leon/Development/Source/HomingBox/gae/sqlalchemy/pool.py", line 368, in __connect
connection = self.__pool._creator()
File "/home/leon/Development/Source/HomingBox/gae/sqlalchemy/engine/strategies.py", line 80, in connect
return dialect.connect(*cargs, **cparams)
File "/home/leon/Development/Source/HomingBox/gae/sqlalchemy/engine/default.py", line 279, in connect
return self.dbapi.connect(*cargs, **cparams)
File "/home/leon/Development/google_appengine/google/storage/speckle/python/api/rdbms_googleapi.py", line 183, in __init__
super(GoogleApiConnection, self).__init__(*args, **kwargs)
File "/home/leon/Development/google_appengine/google/storage/speckle/python/api/rdbms.py", line 810, in __init__
self.OpenConnection()
File "/home/leon/Development/google_appengine/google/storage/speckle/python/api/rdbms.py", line 832, in OpenConnection
self.SetupClient()
File "/home/leon/Development/google_appengine/google/storage/speckle/python/api/rdbms_googleapi.py", line 193, in SetupClient
self._client = RdbmsGoogleApiClient(**kwargs)
File "/home/leon/Development/google_appengine/google/storage/speckle/python/api/rdbms_googleapi.py", line 106, in __init__
rdbms.OAUTH_CREDENTIALS_PATH)
File "/usr/lib/python2.7/posixpath.py", line 268, in expanduser
import pwd
File "/home/leon/Development/google_appengine/google/appengine/tools/devappserver2/python/sandbox.py", line 827, in load_module
raise ImportError
Any help is much appreciated

Answer 1

Here's my hypothesis, based on the stack trace -- when the application can't find your HOME directory, it attempts to import pwd and get the home directory information that way. The application is trying to call this bit of code in posixpath.py:
if 'HOME' not in os.environ:
import pwd
userhome = pwd.getpwuid(os.getuid()).pw_dir
else:
userhome = os.environ['HOME']
Except, I don't think that GAE will allow pwd to be imported for security reasons. The sandbox environment doesn't look to have it included in its whitelist of allowed modules, and raises an ImportError if the modules aren't in that list.
If I attempt to just do an import pwd inside of a regular handler module, GAE won't allow it.