tornado.gen provides utilities for defining and calling coroutines. We use several of these utilities in the Motor project, including but possible not limited to:

• gen.coroutine - this has been superseded by async def
• yield - though not really a tornado-specific thing, the use of this keyword to await coroutines was a programming paradigm encouraged by older tornado versions
• gen.Return - starting in Python 3.5 coroutines can simply return values without needing to wrap them as was done by this helper

With the demise of Python 3.4- support, we should remove these outdated patterns from our codebase.