Check out Sanic if you want an async python framework with a similar API to flask

Its pretty hard to beat Tornado's api, IMHO. Its a really rich api for how simple and quick it is to learn. Flask is a definite downgrade to me, when it comes to the api.

But Flask wins hands down on the richness of its ecosystem.

Most of the "Flask ecosystem" are wrappers for some generic Python libraries which can easily be introduced to any other framework: SQLAlchemy for RDBMS abstraction and ORM, Jinja2 for templating, and so on.

Do you find Golang to be that much harder to develop in, or is it that Python has libraries whose equivalents are missing in Golang? When would you actually choose one over the other?

Python is generally less to type. Go isn't hard, per se, but it is statically typed and tends to be a bit more verbose.

For me: Python if there's a specific library I want to use, I'm just hacking out a proof of concept, or I'm working with text.

Golang for higher performance, concurrency, stream processing, and cryptography (it has good libraries for that kind of stuff).