getting assert error

[himanshu4code]

ERROR:tornado.application:Error in connection callback
Traceback (most recent call last):
File "/home/ongraph/Desktop/botuserv/lib/python3.7/site-packages/tornado/tcpserver.py", line 327, in _handle_connection
future = self.handle_stream(stream, address)
File "/home/ongraph/Desktop/botuserv/lib/python3.7/site-packages/tornado/httpserver.py", line 229, in handle_stream
conn.start_serving(self)
File "/home/ongraph/Desktop/botuserv/lib/python3.7/site-packages/tornado/http1connection.py", line 810, in start_serving
self.stream.io_loop.add_future(fut, lambda f: f.result())
File "/home/ongraph/Desktop/botuserv/lib/python3.7/site-packages/tornado/ioloop.py", line 693, in add_future
assert is_future(future)
AssertionError

when i checked i found out that future get object of Http1ServerConnection.
<Task pending coro=<HTTP1ServerConnection._server_request_loop() >>

[bdarnell]

That's a Task object, and asyncio.Task is a subclass of asyncio.Future, so this should have worked. I'm not sure what could cause something like this. Are you perhaps using a third-party event loop implementation like uvloop?

[dogukankotan]

+1 for me
I'm using Flask and Tornado. The code blocks working, however it gives AssertionError at the background.

Flask==1.0.3
tornado==6.0.3

import asyncio
import nest_asyncio
nest_asyncio.apply(loop=asyncio.get_event_loop())

[ploxiln]

so it seems there's this thing that people try to use: https://github.com/erdewit/nest_asyncio

[bdarnell]

@dogukankotan What's the exact error? Is it the same one as @himanshu4code or something different?

I don't really trust nest_asyncio. Tornado has not been written with reentrant event loops in mind. If you think you need a reentrant event loop, I recommend the two-thread solution from #2798 (comment) instead.

[dogukankotan]

I fixed the issue downgrade to 4.5.3.
@bdarnell yes same error. In my flask project there are some healthcheck methods work in async. So, I think new version of Tornado uses its event loop.

[bdarnell]

Closing since it sounds like this was caused by nest_asyncio. Feel free to reopen with more details if that's not the case.

[maartenbreddels]

FYI: In vaex I solve it by patching Tornado:
https://github.com/vaexio/vaex/blob/10e1d5077021a0590d3750d62d4d56a27a84af82/packages/vaex-core/vaex/asyncio.py

I opened an issue at erdewit/nest_asyncio#23 but it's neither's fault I think, it's just on the edge of what is possible.