sys.set_coroutine_wrapper will be removed in Python 3.8

[encukou]

• uvloop version: master (cbbac15)
• Python version: 3.8.0b1
• Cython version: 0.29.10 (updated for Python 3.8 support)
• Platform: Fedora
• Can you reproduce the bug with PYTHONASYNCIODEBUG in env?: yes

The function "sys.set_coroutine_wrapper", which was provisionally added to Python 3.5 and deprecated in Python 3.7, will be removed in Python 3.8. If uvloop needs it, now is the last chance to make the case for it.

When compiled with Python 3.8.0b1, uvloop fails to import:

Python 3.8.0b1 (default, Jun  5 2019, 14:47:51) 
[GCC 9.1.1 20190503 (Red Hat 9.1.1-1)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import uvloop
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/pviktori/dev/uvloop/uvloop/__init__.py", line 7, in <module>
    from .loop import Loop as __BaseLoop  # NOQA
  File "uvloop/includes/stdlib.pxi", line 119, in init uvloop.loop
    cdef sys_set_coroutine_wrapper = sys.set_coroutine_wrapper
AttributeError: module 'sys' has no attribute 'set_coroutine_wrapper'

[1st1]

No, we don't need it. We'll have to fix the compatibility with 3.8 at some point though.

[hroncok]

AFAIK It's only used conditionally in here:

uvloop/uvloop/loop.pyx

Lines 1055 to 1087 in 46c5e9e

	if PY37:
	if enabled:
	self._coroutine_origin_tracking_saved_depth = (
	sys.get_coroutine_origin_tracking_depth())
	sys.set_coroutine_origin_tracking_depth(
	DEBUG_STACK_DEPTH)
	else:
	sys.set_coroutine_origin_tracking_depth(
	self._coroutine_origin_tracking_saved_depth)
	self._coroutine_debug_set = enabled
	else:
	wrapper = aio_debug_wrapper
	current_wrapper = sys_get_coroutine_wrapper()
	if enabled:
	if current_wrapper not in (None, wrapper):
	_warn_with_source(
	"loop.set_debug(True): cannot set debug coroutine "
	"wrapper; another wrapper is already set %r" %
	current_wrapper, RuntimeWarning, self)
	else:
	sys_set_coroutine_wrapper(wrapper)
	self._coroutine_debug_set = True
	else:
	if current_wrapper not in (None, wrapper):
	_warn_with_source(
	"loop.set_debug(False): cannot unset debug coroutine "
	"wrapper; another wrapper was set %r" %
	current_wrapper, RuntimeWarning, self)
	else:
	sys_set_coroutine_wrapper(None)
	self._coroutine_debug_set = False

[hroncok]

My Cython knowledge is limited here. I wanted to do something like:

from cpython.version cimport PY_VERSION_HEX
...

IF PY_VERSION_HEX > 0x03080000:
    cdef sys_set_coroutine_wrapper = sys.set_coroutine_wrapper
    cdef sys_get_coroutine_wrapper = sys.get_coroutine_wrapper

But apparently, Cython determines this IF when cythonzing and hence it cannot work (Compile-time name 'PY_VERSION_HEX' not defined.

On the other hand, cdefs are not possible in regular if:

from cpython.version cimport PY_VERSION_HEX
...

if PY_VERSION_HEX < 0x03080000:
    cdef sys_set_coroutine_wrapper = sys.set_coroutine_wrapper
    cdef sys_get_coroutine_wrapper = sys.get_coroutine_wrapper

Gets to:

if PY_VERSION_HEX < 0x03080000:
    cdef sys_set_coroutine_wrapper = sys.set_coroutine_wrapper
        ^

uvloop/includes/stdlib.pxi:123:9: cdef statement not allowed here

Id like to make an actual C #if in there, but don't know how.

EDIT:

Trying with:

cdef sys_set_coroutine_wrapper = getattr(sys, 'set_coroutine_wrapper', None)
cdef sys_get_coroutine_wrapper = getattr(sys, 'get_coroutine_wrapper', None)

[hroncok]

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