What’s New in Cython 3.0? A Deep Dive into Its Major Features and Impact

Cython 3.0 has been officially released, announced by its co‑developer Dr. Stefan Behnel after nearly five years of development. The new version defaults to Python 3 syntax and semantics and brings many enhancements.

Key Improvements

Dropping support for the long‑obsolete Python 2 and adding compatibility up to the upcoming CPython 3.12 (experimental).

Full alignment of Cython semantics with Python 3 for division, exponentiation, print, classes, typing and indexing, reversible via the language_level compiler directive.

Enhanced exception handling: C functions generated by Cython now raise exceptions by default, and missing except declarations in signatures trigger errors, though this behavior can be disabled.

Significant upgrades to C and C++ interoperability.

The release also fixes a compatibility bug that broke installations of tools such as the AWS CLI, caused by a dependency chain involving PyYAML; a build constraint was added to keep Cython 2.x functional.

Originally named Pyrex in 2002, Cython is now over 21 years old and has become a cornerstone of the Python data ecosystem, used in projects ranging from Mars rovers to large‑scale Django sites and climate models.