PythonSQLAlchemy

Python SQLAlchemy is a Python toolkit and object-relational mapper (ORM) that provides a high-level interface for working with relational databases. Developed by Michael Bayer, it aims to combine the full power of SQL with a Pythonic, expressive API. SQLAlchemy supports multiple database backends through dialects and is widely used in Python applications ranging from small scripts to large web services.

SQLAlchemy consists of two main components: Core and ORM. The Core offers a SQL expression language, a connection and transaction system, and schema metadata. The ORM builds on top of Core to map Python classes to database tables, enabling declarative or classical mapping. The Engine establishes database connections, while Session implements a unit-of-work pattern for transactions and queries. MetaData describes the database schema.

Key design goals include database portability, flexibility, and explicit control over SQL generation. The library supports both explicit SQL construction and high-level ORM queries, with features such as lazy and eager loading of relationships, identity maps, and rich transaction management. It works with many backends (for example SQLite, PostgreSQL, MySQL, Oracle, and SQL Server) via dialects, and aligns with the modern 2.x API.

Common use cases include web application backends, data access layers in services, and migration-enabled projects when paired with tools like Alembic. SQLAlchemy is often used directly or through higher-level wrappers in web frameworks such as Flask, where an extension can provide integration with the ORM while remaining usable independently.