# Pastebin vlmO4zlN
(craton) ubuntu@ubuntu-xenial:~/craton$ python3.5 t-rbac.py 
/home/ubuntu/craton/lib/python3.5/site-packages/sqlalchemy/orm/mapper.py:1228: SAWarning: Could not assemble any primary keys for locally mapped table 'users' - no rows will be persisted in this Table.
  % self.local_table.description)
Traceback (most recent call last):
  File "t-rbac.py", line 9, in <module>
    engine = create_engine(sys.argv[1] if len(sys.argv) > 1 else 'mysql+pymysql://craton:craton@localhost/craton', echo=True)
  File "/home/ubuntu/craton/lib/python3.5/site-packages/sqlalchemy/engine/__init__.py", line 386, in create_engine
    return strategy.create(*args, **kwargs)
  File "/home/ubuntu/craton/lib/python3.5/site-packages/sqlalchemy/engine/strategies.py", line 75, in create
    dbapi = dialect_cls.dbapi(**dbapi_args)
  File "/home/ubuntu/craton/lib/python3.5/site-packages/sqlalchemy/dialects/mysql/pymysql.py", line 49, in dbapi
    return __import__('pymysql')
ImportError: No module named 'pymysql'