asyncio: enable debug mode when -X dev is used

[vstinner]

BPO	32047
Nosy	@vstinner, @1st1
PRs	bpo-32047: -X dev enables asyncio debug mode #4418
Files	block_loop.py

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2017-11-20.15:14:29.505>
created_at = <Date 2017-11-16.11:50:52.830>
labels = ['3.7', 'expert-asyncio']
title = 'asyncio: enable debug mode when -X dev is used'
updated_at = <Date 2017-11-20.15:14:29.504>
user = 'https://github.com/vstinner'

bugs.python.org fields:

activity = <Date 2017-11-20.15:14:29.504>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2017-11-20.15:14:29.505>
closer = 'vstinner'
components = ['asyncio']
creation = <Date 2017-11-16.11:50:52.830>
creator = 'vstinner'
dependencies = []
files = ['47269']
hgrepos = []
issue_num = 32047
keywords = ['patch']
message_count = 3.0
messages = ['306353', '306360', '306552']
nosy_count = 2.0
nosy_names = ['vstinner', 'yselivanov']
pr_nums = ['4418']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue32047'
versions = ['Python 3.7']

[vstinner]

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

[vstinner]

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

[vstinner]

New changeset 44862df by Victor Stinner in branch 'master':
bpo-32047: -X dev enables asyncio debug mode (bpo-4418)
44862df