Hello, Flask

Flask: the smallest possible web framework

Writing raw HTTP text by hand would be miserable. Flask is a Python micro-framework — a small library that listens for HTTP requests, matches the path to a function you wrote, calls it, and turns whatever you return into a proper HTTP response.

"Micro" means it does almost nothing for you beyond that. No database, no validation, no built-in auth. You'll feel every one of those gaps in the next module — that's the point. FastAPI (Stage D) fills them in; Flask makes you appreciate why.