I second FastAPI! In my mind it's, "Flask, but better." The killer feature in my mind is that it leverages type hinting and dataclasses, using Pydantic, to take away a lot of the grindyy, boilerplate parts of writing an API, like type checking, dependency injection, generating good error messages, generating API documentation, ...

Even when I'm not using FastAPI now, I use Pydantic everywhere. Types in Python, while not nearly as useful as in a strongly typed language, are a dream come true.