cython report bug: expected an identifier - cython

Question

I am using cython to convert py file to pyd file.
My test code is:
# funcA.py
class Window:
def exec(self):
pass
pass
And the setup.py file is:
#setup.py
from setuptools import setup
from distutils.extension import Extension
from Cython.Distutils import build_ext
ext_modules = [
Extension('funcA', ['funcA.py']),
]
setup(
name='App',
ext_modules=ext_modules,
include_dirs=["App"],
cmdclass={'build_ext': build_ext},
)
After python setup.py build_ext --inplace, a bug is reported:
Error compiling Cython file:
------------------------------------------------------------
...
class Window:
def exec(self):
^
------------------------------------------------------------
funcA.py:4:8: Expected an identifier
building 'funcA' extension
"C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\bin\HostX86\x64\cl.exe" /c /nologo /O2 /W3 /GL /DNDEBUG /MD -IApp -ID:\Anaconda3\envs\work\include -ID:\Anaconda3\envs\work\Includ
e "-IC:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\ATLMFC\include" "-IC:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\include" "-IC:\Prog
ram Files (x86)\Windows Kits\10\include\10.0.19041.0\ucrt" "-IC:\Program Files (x86)\Windows Kits\10\include\10.0.19041.0\shared" "-IC:\Program Files (x86)\Windows Kits\10\include\10.0.19041.0\um" "-IC:\Program Files (x
86)\Windows Kits\10\include\10.0.19041.0\winrt" "-IC:\Program Files (x86)\Windows Kits\10\include\10.0.19041.0\cppwinrt" /TcfuncA.c /Fobuild\temp.win-amd64-cpython-39\Release\funcA.obj
funcA.c
funcA.c(1): fatal error C1189: #error: Do not use this file, it is the result of a failed Cython compilation.
error: command 'C:\\Program Files (x86)\\Microsoft Visual Studio\\2019\\Community\\VC\\Tools\\MSVC\\14.29.30133\\bin\\HostX86\\x64\\cl.exe' failed with exit code 2
But, if I replace the funcA.py to:
#new funcA.py
class Window:
pass
Everything is OK.
Why exec function would couse this bug?
Any suggestion is appreciated~~~
------------- update --------------------------------
Thanks #DavidW's suggestion.
The solution is adding #cython: language_level=3 on the top of script.

Answer 1

Depending on what Cython version you're using (you don't say...) Cython defaults to Python 2 behaviour. In Python 2 exec was a keyword, so cannot be used as a function name.
Either:
pick a different function name,
put Cython in Python 3-like mode by setting language_level to 3. Bear in mind this may change some other things (e.g. print, the scope of list comprehensions, ...)
Use Cython 3 alpha version where it does default to Python 3 semantics by default.