Python: async def

async def functions return coroutine objects

A function declared with async def returns a coroutine object:

import asyncio

async def coro_func(): pass

coro_obj = coro_func()

print(type(coro_obj)) # <class 'coroutine'>

asyncio.run(coro_obj)

PEP 492 lists some properties of coroutines:

async def functions are always coroutines, even if they do not contain await expressions.
It is a SyntaxError to have yield or yield from expressions in an async function.
Internally, two new code object flags were introduced: CO_COROUTINE is used to mark native coroutines (defined with new syntax); O_ITERABLE_COROUTINE is used to make generator-based coroutines compatible with native coroutines (set by types.coroutine() function).
Regular generators, when called, return a generator object; similarly, coroutines return a coroutine object.
StopIteration exceptions are not propagated out of coroutines, and are replaced with a RuntimeError. For regular generators such behavior requires a future import (see PEP 479).
When a native coroutine is garbage collected, a RuntimeWarning is raised if it was never awaited on.