The Basilisk Journal

Typing

Writing collected under this topic.

Python type shapes passing through a conditional evaluator and expanding into a mapped type lattice

Deep dives July 16, 2026

PEP 827 Explained: Conditional and Mapped Types for Python

PEP 827 is Python's boldest attempt yet at TypeScript-style type manipulation. It is powerful, controversial, and a serious implementation challenge for every Python type checker.