RuntimeWarning on Python 3.8

[Harmon758]

Description
Attempting to import multidict using Python 3.8.0a4 3.8.0b1 raises a SystemError 3.8.0b2 causes a RuntimeWarning to occur.

Reproduction Steps

1. Use Python 3.8.0a4 3.8.0b1 3.8.0b2
2. import multidict
3. Observe traceback warning

Expected Behavior
Successful import
No warning

Traceback

>>> import multidict
<frozen importlib._bootstrap>:219: RuntimeWarning: builtins.type size changed, may indicate binary incompatibility. Expected 864 from C header, got 880 from PyObject

Traceback (most recent call last):
File "", line 1, in
File "C:\Program Files\Python38\lib\site-packages\multidict_init_.py", line 23, in
from ._multidict import (MultiDictProxy,
SystemError: c:_work\14\s\objects\codeobject.c:131: bad argument to internal function

Python Version
Python 3.8.0a4 (v3.8.0a4:c1004b8546, May 7 2019, 13:53:12) [MSC v.1916 64 bit (AMD64)] on win32
Python 3.8.0b1 (tags/v3.8.0b1:3b5deb0116, Jun 4 2019, 19:52:55) [MSC v.1916 64 bit (AMD64)] on win32
Python 3.8.0b2 (tags/v3.8.0b2:21dd01d, Jul 4 2019, 16:00:09) [MSC v.1916 64 bit (AMD64)] on win32

multidict Version
multidict 4.5.2

Additional Context
This seems to be caused by changes to PyCode_New as part of the implementation of PEP 570:
python/cpython@8c77b8c#diff-e3862c228cffe90385cf9f14529868fe (python/cpython#12701)

bpo-37221 has reverted PyCode_New to be a backwards compatible wrapper for a new PyCode_NewEx with python/cpython@cb083f7 (python/cpython#13959, python/cpython#14505).
The handling for this change was added in Cython 0.29.11 with cython/cython@9b6a02f (cython/cython#3009) and fixed in Cython 0.29.12 with cython/cython@0d88839 (cython/cython#3031, cython/cython#3034).

Updating to Cython 0.29.12 should now resolve this issue.

[asvetlov]

Thanks for the report!

[webknjaz]

Looks like Cython 0.29.12 fixes it.

[Harmon758]

The import succeeds and only a RuntimeWarning occurs now with Python 3.8.0b2.
Cython 0.29.12 should resolve that issue (as well as the SystemError with Python 3.8.0a4 and 3.8.0b1).
I've updated the issue accordingly.

[webknjaz]

Solved by #355.