In JS, Python and similarly built systems async is inherently coupled to an inversion of control. When you write (Python): await sock.write("fooooooo") w

In JS, Python and similarly built systems async is inherently coupled to an inversion of control. When you write (Python): await sock.write("fooooooo") write will, after several layers of abstractions and wrappers, look like this (on a reactor/readiness-oriented system): def write(self, data): while data: try: written = self._socket.write(data) except EWOULDBLOCK, EAGAIN: yield 'writable', self._socket data = data[written:] "yield" here means to pass a bit of data up to the event loop (neé coroutine scheduler), and that event loop will watch (using select/epoll) for that socket to become writable and then hand control back. Because this inversion of control doesn't happen unless you (usually) explicitly wrap a coroutine (e.g. asyncio.run_until_complete) with an event loop, you can't just call a coroutine. It doesn't know when to resume in these designs, and your synchronous function doesn't know how to, either.