May also be worth pointing out that even in the case of only calling set_result once, _done_callbacks still has _chain_future in it:


import asyncio
import concurrent.futures


f = concurrent.futures.Future()
async_f = asyncio.wrap_future(f)

f.set_result(1)
loop = asyncio.get_event_loop()
print(loop.run_until_complete(async_f))
print(f._done_callbacks)


>>> 1
>>> [<function _chain_future.<locals>._call_set_state at 0x7f1687f3c620>]


Should that be cleared by that point?