Task.current_task(None) returns unexpected result

[1st1]

BPO	29271
Nosy	@methane, @1st1, @lelit, @azazel75
PRs	bpo-29271: Fix Task.current_task and Task.all_tasks to accept None. #406 bpo-29271: Fix Task.current_task and Task.all_tasks to accept None. #413 [Do Not Merge] Sample of CPython life with blurb. #703 [Do Not Merge] Convert Misc/NEWS so that it is managed by towncrier #552
Files	task.patch

^{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 = 'https://github.com/1st1'
closed_at = <Date 2017-03-03.23:10:28.529>
created_at = <Date 2017-01-13.22:11:24.834>
labels = ['type-bug', '3.7', 'expert-asyncio']
title = 'Task.current_task(None) returns unexpected result'
updated_at = <Date 2017-03-31.16:36:33.267>
user = 'https://github.com/1st1'

bugs.python.org fields:

activity = <Date 2017-03-31.16:36:33.267>
actor = 'dstufft'
assignee = 'yselivanov'
closed = True
closed_date = <Date 2017-03-03.23:10:28.529>
closer = 'yselivanov'
components = ['asyncio']
creation = <Date 2017-01-13.22:11:24.834>
creator = 'yselivanov'
dependencies = []
files = ['46284']
hgrepos = []
issue_num = 29271
keywords = ['patch']
message_count = 6.0
messages = ['285445', '285447', '285448', '285456', '288855', '290338']
nosy_count = 4.0
nosy_names = ['methane', 'yselivanov', 'lelit', 'azazel']
pr_nums = ['406', '413', '703', '552']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue29271'
versions = ['Python 3.6', 'Python 3.7']

[1st1]

Quoting Alberto Berdi from python-tulip mailing list:

working with the Python 3.6 asyncio implemented in C, i've got what is
for me a strange behavior of the asyncio.Task.current task
function. Executing the following test:

 import asyncio

 async def coro():
     print(asyncio.Task.current_task())
     print(asyncio.Task.current_task(None))
     print(asyncio.Task.current_task(loop=asyncio.get_event_loop()))

 loop = asyncio.get_event_loop()
 loop.run_until_complete(coro())

in Py3.5, I obtain the result:

<Task pending coro=<coro() running at test_task.py:4> cb=[_run_until_complete_cb() at /usr/lib/python3.5/asyncio/base_events.py:176]>
<Task pending coro=<coro() running at test_task.py:5> cb=[_run_until_complete_cb() at /usr/lib/python3.5/asyncio/base_events.py:176]>
<Task pending coro=<coro() running at test_task.py:6> cb=[_run_until_complete_cb() at /usr/lib/python3.5/asyncio/base_events.py:176]>

In Py3.6, i get:

<Task pending coro=<coro() running at test_task.py:4> cb=[_run_until_complete_cb() at /usr/lib/python3.6/asyncio/base_events.py:176]>
None
<Task pending coro=<coro() running at test_task.py:6> cb=[_run_until_complete_cb() at /usr/lib/python3.6/asyncio/base_events.py:176]>

What's going on here? It's still right to expect the same result from the three calls or something has changed?
The documentation for the Task.current_task() function seems unchanged between the two version.

My python3.6 has version:

$ python3.6 -VV
Python 3.6.0 (default, Dec 29 2016, 04:29:02) 
[GCC 6.2.1 20161215]

[lelit]

FWIW, the problem afflicts other functions, for example the following script exhibits a similar difference:

import asyncio

async def coro():
    print(asyncio.Task.all_tasks())
    print(asyncio.Task.all_tasks(None))

loop = asyncio.get_event_loop()
loop.run_until_complete(coro())

[lelit]

Yay, Yury is too fast!! :-)

[methane]

LGTM

[1st1]

New changeset 13802a3 by Yury Selivanov in branch '3.6':
bpo-29271: Fix Task.current_task and Task.all_tasks to accept None. (#406)
13802a3

[1st1]

New changeset 8d26aa9 by Yury Selivanov in branch 'master':
bpo-29271: Fix Task.current_task and Task.all_tasks to accept None. (#406)
8d26aa9