[Side A] Why BytesIO Isn't Enough — Building a Python In-Memory FS Library

Author's Note: I am a software engineer based in Japan. This article is an English translation (with AI assistance for clarity) of a practical technical guide originally written for the Japanese developer community platform, Qiita. Recently, I introduced my project, D-MemFS , on Reddit (r/Python) , where it sparked intense discussions. This response confirmed that in-memory I/O bottlenecks and OOM crashes are truly universal pain points for developers everywhere. Therefore, I decided to cross the language barrier and share these concrete solutions globally. 🧭 About this Series: The Two Sides of Development In Japan, I publish this series across two distinct platforms to serve different developer needs. To provide the complete picture here on Dev.to, I've brought them together as two "Sides": Side A (Practical / originally on Qiita): Focuses on the "How" . Implementation details, benchmarks, and concrete solutions for practical use cases. Side B (Philosophy / originally on Zenn): Focuse