h2 is a HTTP/2 protocol stack, written entirely in Python. The goal of h2 is to be a common HTTP/2 stack for the Python ecosystem, usable in all programs regardless of concurrency model or environment. To achieve this, h2 is entirely self-contained: it does no I/O of any kind, leaving that up to a wrapper library to control. This ensures that it can seamlessly work in all kinds of environments, from single-threaded code to Twisted.