Accessing relational database systems from Python is straighforward. The Python standard library comes with a simple in-memory relational database system SQLite via de sqlite3 module. Other RDBMS can be accessed similarly using SQLAlchemy.

However, SQLAlchemy also support an object-relational mapping approach, which is also illustrated by sample code.

1. ExperimentDB: Example of SQLAlchemy's object-relational mapping, illustrating declarative schema definition, bidirectional associations and back references. Also adds a shell to manipulate the database using a domain specific language.
2. Orm: simple illustration of SQLAlchemy's ORM approach.
3. StraightSql: Example of how to interact with a relation database (SQLite3) using SQL from Python.