Hi All, I was recently migrating uvloop to cython3 [1]. Unfortunately, after switching to cython3, uvloop testsuite fails [2]. I am puzzled mainly about following error: ====================================================================== ERROR: test_process_delayed_stdio__paused__no_stdin (test_process.Test_UV_Process_Delayed) ---------------------------------------------------------------------- Traceback (most recent call last): File "/home/runner/work/uvloop/uvloop/tests/test_process.py", line 938, in test_process_delayed_stdio__paused__no_stdin __uvloop_sleep_after_fork=True)) File "uvloop/loop.pyx", line 1517, in uvloop.loop.Loop.run_until_complete return future.result() File "/home/runner/work/uvloop/uvloop/tests/test_process.py", line 911, in run_sub **kwargs) File "uvloop/loop.pyx", line 2808, in subprocess_shell return await self.__subprocess_run(protocol_factory, args, shell=True, File "uvloop/loop.pyx", line 2734, in uvloop.loop.Loop._Loop__subprocess_run @cython.iterable_coroutine TypeError: _Loop__subprocess_run() got an unexpected keyword argument '__uvloop_sleep_after_fork' ====================================================================== ERROR: test_process_delayed_stdio__paused__stdin_pipe (test_process.Test_UV_Process_Delayed) ---------------------------------------------------------------------- Traceback (most recent call last): File "/home/runner/work/uvloop/uvloop/tests/test_process.py", line 919, in test_process_delayed_stdio__paused__stdin_pipe __uvloop_sleep_after_fork=True)) File "uvloop/loop.pyx", line 1517, in uvloop.loop.Loop.run_until_complete return future.result() File "/home/runner/work/uvloop/uvloop/tests/test_process.py", line 911, in run_sub **kwargs) File "uvloop/loop.pyx", line 2808, in subprocess_shell return await self.__subprocess_run(protocol_factory, args, shell=True, File "uvloop/loop.pyx", line 2734, in uvloop.loop.Loop._Loop__subprocess_run @cython.iterable_coroutine TypeError: _Loop__subprocess_run() got an unexpected keyword argument '__uvloop_sleep_after_fork' The issue is regarding calling this method: https://github.com/MagicStack/uvloop/blob/1dd40f17f3b0d37e3779b6ad5041bab335... When the same code base is compiled in Cython 0.29.X and the test suite is run, there is no such error. I tried to create a simple reproducer but failed. What do you think? Is it regression in Cython 3.0? Do you have any hint where the root cause can be? If everything fails, I will try to bisect the issue. Matus [1] https://github.com/MagicStack/uvloop/pull/534 [2] https://github.com/MagicStack/uvloop/pull/534/checks