The bpo-32043 added a new "developer mode" enabled with the new -X dev command line option. I propose to enable asyncio debug mode with the global Python "developer mode". If an asyncio application is correctly written, the single side effect of -X dev would be to log "Executing ... took ... seconds" if a handle took longer than 100 ms. Well, a handle should *not* take longer than 100 ms. So maybe it's ok to start logging such events in the "developer mode", no? Example with attached block_loop.py script which blocks the event loop. (1) This command doesn't display anything: haypo@selma$ ./python block_loop.py (2) In developer mode, the warning a emitted to warn the developer about the bug: $ ./python -X dev block_loop.py Executing <Task finished coro=<block_loop() done, defined at block_loop.py:4> result=None created at /home/haypo/prog/python/master/Lib/asyncio/base_events.py:444> took 1.002 seconds

I sent an email about this change to python-dev: https://mail.python.org/pipermail/python-dev/2017-November/150572.html

 New changeset 44862df2eeec62adea20672b0fe2a5d3e160569e by Victor Stinner in branch 'master': bpo-32047: -X dev enables asyncio debug mode (#4418) https://github.com/python/cpython/commit/44862df2eeec62adea20672b0fe2a5d3e160569e