Mujoco-py is incompatible with cython 3 (Cannot assign type 'void (const char *) except * nogil' to 'void (*)(const char *) noexcept nogil)

[pseudo-rnd-thoughts]

Describe the bug
Cannot assign type 'void (const char *) except * nogil' to 'void (*)(const char *) noexcept nogil'

To Reproduce
Install cpython 3.0.0, import mujoco-py

Expected behavior
mujoco-py compiles

Error Messages
From gymnasium's CI

tests/wrappers/test_passive_env_checker.py:9: in <module>
    from tests.envs.test_envs import PASSIVE_CHECK_IGNORE_WARNING
<frozen importlib._bootstrap>:991: in _find_and_load
    ???
<frozen importlib._bootstrap>:975: in _find_and_load_unlocked
    ???
<frozen importlib._bootstrap>:671: in _load_unlocked
    ???
../lib/python3.8/site-packages/_pytest/assertion/rewrite.py:168: in exec_module
    exec(co, module.__dict__)
tests/envs/test_envs.py:10: in <module>
    from tests.envs.utils import (
tests/envs/utils.py:34: in <module>
    all_testing_initialised_envs: List[Optional[gym.Env]] = [
tests/envs/utils.py:35: in <listcomp>
    try_make_env(env_spec) for env_spec in gym.envs.registry.values()
tests/envs/utils.py:22: in try_make_env
    return env_spec.make(disable_env_checker=True).unwrapped
gymnasium/envs/registration.py:130: in make
    return make(self, **kwargs)
gymnasium/envs/registration.py:756: in make
    env_creator = load_env_creator(env_spec.entry_point)
gymnasium/envs/registration.py:545: in load_env_creator
    mod = importlib.import_module(mod_name)
../lib/python3.8/importlib/__init__.py:127: in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
gymnasium/envs/mujoco/__init__.py:1: in <module>
    from gymnasium.envs.mujoco.mujoco_env import MujocoEnv, MuJocoPyEnv  # isort:skip
gymnasium/envs/mujoco/mujoco_env.py:13: in <module>
    import mujoco_py
/mujoco-py/mujoco_py/__init__.py:2: in <module>
    from mujoco_py.builder import cymj, ignore_mujoco_warnings, functions, MujocoException
/mujoco-py/mujoco_py/builder.py:504: in <module>
    cymj = load_cython_ext(mujoco_path)
/mujoco-py/mujoco_py/builder.py:110: in load_cython_ext
    cext_so_path = builder.build()
/mujoco-py/mujoco_py/builder.py:226: in build
    built_so_file_path = self._build_impl()
/mujoco-py/mujoco_py/builder.py:278: in _build_impl
    so_file_path = super()._build_impl()
/mujoco-py/mujoco_py/builder.py:239: in _build_impl
    dist.ext_modules = cythonize([self.extension])
../lib/python3.8/site-packages/Cython/Build/Dependencies.py:1134: in cythonize
    cythonize_one(*args)
../lib/python3.8/site-packages/Cython/Build/Dependencies.py:1301: in cythonize_one
    raise CompileError(None, pyx_file)
E   Cython.Compiler.Errors.CompileError: /mujoco-py/mujoco_py/cymj.pyx
------------------------------- Captured stdout --------------------------------
Compiling /mujoco-py/mujoco_py/cymj.pyx because it changed.
[1/1] Cythonizing /mujoco-py/mujoco_py/cymj.pyx
------------------------------- Captured stderr --------------------------------

Error compiling Cython file:
------------------------------------------------------------
...
    See c_warning_callback, which is the C wrapper to the user defined function
    '''
    global py_warning_callback
    global mju_user_warning
    py_warning_callback = warn
    mju_user_warning = c_warning_callback
                       ^
------------------------------------------------------------

/mujoco-py/mujoco_py/cymj.pyx:92:23: Cannot assign type 'void (const char *) except * nogil' to 'void (*)(const char *) noexcept nogil'

Error compiling Cython file:
------------------------------------------------------------
...
    See c_warning_callback, which is the C wrapper to the user defined function
    '''
    global py_error_callback
    global mju_user_error
    py_error_callback = err_callback
    mju_user_error = c_error_callback
                     ^
------------------------------------------------------------

/mujoco-py/mujoco_py/cymj.pyx:127:21: Cannot assign type 'void (const char *) except * nogil' to 'void (*)(const char *) noexcept nogil'

[JayanthRR]

Facing the same issue.

[ChengDaHaI]

Same issue on my side

[pseudo-rnd-thoughts]

I solved it with pip install "cython<3"

[fyqqyf]

Same issue on my side

[AdilZouitine]

Same

[ezhang7423]

TYSM for figuring this out, wasted 3 hours today

[fyqqyf]

TYSM for figuring this out, wasted 3 hours today

4 hours and 5 times recreate virtual environments 😇

[alafumee]

already have Cython==0.29.36 but the same error exists when pip install mujoco_py==2.0.2.7

[qodfathr]

already have Cython==0.29.36 but the same error exists when pip install mujoco_py==2.0.2.7

Same

[ezhang7423]

I am using mujoco-py==1.50.1.68

[qodfathr]

I cannot tell if this is directly related to cython 3 or not. I have 0.29.36 installed (and I've tried many versions from 0.27.2 on up) and the same error is occurring even on mujoco_py==2.0.2.13. I tried to determine if a patch to the underlying c++ compiler was at fault, but that does not seem to be the case.