Local MySQLdb connection fails with AttributeError for paramstyle when running GAE development server
google-app-engine, google-cloud-sql, python, sqlalchemy
Solution
This means the `MySQLdb` module is missing and failed to import. The GAE SDK does not itself come with the MySQLdb client library; install MySQLdb (as instructed in the SDK documentation):
venv/bin/pip install mysql-python
or use your OS package manager to install MySQLdb in your system python.
The error is caused by the Google `google.appengine.api.rdbms_mysqldb` module, acting as a stub, not having a `paramstyle` attribute when `import MySQLdb` fails. A stub `connect()` function is provided that'll raise a more helpful exception, but due to an unfortunate interaction with SQLAlchemy the error there is a lot less informative.
Problem
I'm building a GAE Flask application with Flask-Alchemy, against Cloud SQL, and running `dev_appserver` to test the application as I build it. However, if I set the `SQLALCHEMY_DATABASE_URI` to a `mysql+gaerdbms:///appname?instance=instanceid` URL, I get the following traceback when trying to call `db.create_all()`: ``` Traceback (most recent call last): # earlier lines omitted for brevity File "/Project/app/foo.bar/foo/bar/admin/__init__.py", line 26, in init_db db.create_all() File "/Project/app/distlib/flask_sqlalchemy/__init__.py", line 856, in create_all self._execute_for_all_tables(app, bind, 'create_all') File "/Project/app/distlib/flask_sqlalchemy/__init__.py", line 848, in _execute_for_all_tables op(bind=self.get_engine(app, bind), tables=tables) File "/Project/app/distlib/flask_sqlalchemy/__init__.py", line 797, in get_engine return connector.get_engine() File "/Project/app/distlib/flask_sqlalchemy/__init__.py", line 473, in get_engine self._engine = rv = sqlalchemy.create_engine(info, **options) File "/Project/app/distlib/sqlalchemy/engine/__init__.py", line 332, in create_engine return strategy.create(*args, **kwargs) File "/Project/app/distlib/sqlalchemy/engine/strategies.py", line 69, in create dialect = dialect_cls(**dialect_args) File "/Project/app/distlib/sqlalchemy/dialects/mysql/base.py", line 1986, in __init__ default.DefaultDialect.__init__(self, **kwargs) File "/Project/app/distlib/sqlalchemy/engine/default.py", line 124, in __init__ self.paramstyle = self.dbapi.paramstyle AttributeError: 'module' object has no attribute 'paramstyle' ``` What gives? Why is the (DB-API 2.0 required) `paramstyle` attribute missing?