There are a fairly large number of Python ORM projects. A list of these can be found here: https://wiki.python.org/moin/HigherLevelDatabaseProgramming.
We're going to pick just one of these as an example. We'll use SQLAlchemy because it offers us a number of features and is reasonably popular. As with many things, there's no best; other ORM layers have different advantages and disadvantages.
Because of the popularity of using a relational database to support Web development, Web frameworks often include ORM layers. Django has its own ORM layer, as does web.py. In some cases, we can tease the ORMs out of the larger framework. However, it seems simpler to work with a standalone ORM.
The documentation, installation guide, and code ...