What’s New in SQLAlchemy 2.1?

About this Document

This document describes changes between SQLAlchemy version 2.0 and version 2.1.

Asyncio “greenlet” dependency no longer installs by default

SQLAlchemy 1.4 and 2.0 used a complex expression to determine if the greenlet dependency, needed by the asyncio extension, could be installed from pypi using a pre-built wheel instead of having to build from source. This because the source build of greenlet is not always trivial on some platforms.

Disadantages to this approach included that SQLAlchemy needed to track exactly which versions of greenlet were published as wheels on pypi; the setup expression led to problems with some package management tools such as poetry; it was not possible to install SQLAlchemy without greenlet being installed, even though this is completely feasible if the asyncio extension is not used.

These problems are all solved by keeping greenlet entirely within the [asyncio] target. The only downside is that users of the asyncio extension need to be aware of this extra installation dependency.