Explore a transformative approach to Python's NotImplemented in this 24-minute EuroPython 2023 conference talk. Dive into the Dirty Equals library, created by Pydantic's Samuel Colvin, and discover how it revolutionizes test writing, particularly for APIs. Learn how contributing to this project reshaped the speaker's understanding of NotImplemented, moving beyond its conventional use as a placeholder for unfinished work and unexpected scenarios. Uncover the magic behind using NotImplemented to modify Python's built-in equality operator, and gain fresh insights into language quirks. This talk challenges preconceptions about Python's lesser-known features and demonstrates their potential for innovative programming solutions.