pyfakefs: OSError: [Errno 9] Bad file descriptor in the fake filesystem

Hey folks 👋

I’m facing an issue that seems to be related to pyfakefs, but I’m not 100% sure. While implementing an integration between MetricFlow and Prefect 2.0, I’m using pyfakefs to mock some files I need.

I was able to reproduce the issue with this minimal script:

from prefect import flow


def test_example(fs):

    msg = "This is an example flow"
    
    @flow
    def test_flow():
        return msg
    

    response = test_flow()

    assert response == msg

I’m using pyfakefs==4.6.3 and prefect==2.0b12

Below you can find the trace back generated by pytest:

platform darwin -- Python 3.9.10, pytest-7.1.2, pluggy-1.0.0 -- /Users/alessandro.lollo/.pyenv/versions/3.9.10/envs/prefect-metricflow/bin/python3.9
cachedir: .pytest_cache
rootdir: /Users/alessandro.lollo/dev/prefect-collections/prefect-metricflow, configfile: setup.cfg
plugins: anyio-3.6.1, pyfakefs-4.6.3, asyncio-0.19.0
asyncio: mode=auto
collected 1 item                                                                                                                

tests/test_example.py::test_example FAILED                                                                                [100%]

=========================================================== FAILURES ============================================================
_________________________________________________________ test_example __________________________________________________________

fs = <pyfakefs.fake_filesystem.FakeFilesystem object at 0x10fe72eb0>

    def test_example(fs):
    
        msg = "This is an example flow"
    
        @flow
        def test_flow():
            return msg
    
    
>       response = test_flow()

/Users/alessandro.lollo/dev/prefect-collections/prefect-metricflow/tests/test_example.py:13: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
/Users/alessandro.lollo/.pyenv/versions/3.9.10/envs/prefect-metricflow/lib/python3.9/site-packages/prefect/flows.py:367: in __call__
    return enter_flow_run_engine_from_flow_call(
/Users/alessandro.lollo/.pyenv/versions/3.9.10/envs/prefect-metricflow/lib/python3.9/site-packages/prefect/engine.py:110: in enter_flow_run_engine_from_flow_call
    setup_logging()
/Users/alessandro.lollo/.pyenv/versions/3.9.10/envs/prefect-metricflow/lib/python3.9/site-packages/prefect/logging/configuration.py:66: in setup_logging
    config = load_logging_config(
/Users/alessandro.lollo/.pyenv/versions/3.9.10/envs/prefect-metricflow/lib/python3.9/site-packages/prefect/logging/configuration.py:33: in load_logging_config
    template = string.Template(path.read_text())
/Users/alessandro.lollo/.pyenv/versions/3.9.10/lib/python3.9/pathlib.py:1266: in read_text
    with self.open(mode='r', encoding=encoding, errors=errors) as f:
/Users/alessandro.lollo/.pyenv/versions/3.9.10/lib/python3.9/pathlib.py:1252: in open
    return io.open(self, mode, buffering, encoding, errors, newline,
/Users/alessandro.lollo/.pyenv/versions/3.9.10/envs/prefect-metricflow/lib/python3.9/site-packages/pyfakefs/fake_filesystem.py:5036: in open
    return fake_open(file, mode, buffering, encoding, errors,
/Users/alessandro.lollo/.pyenv/versions/3.9.10/envs/prefect-metricflow/lib/python3.9/site-packages/pyfakefs/fake_filesystem.py:5721: in __call__
    return self.call(*args, **kwargs)
/Users/alessandro.lollo/.pyenv/versions/3.9.10/envs/prefect-metricflow/lib/python3.9/site-packages/pyfakefs/fake_filesystem.py:5778: in call
    file_object, file_path, filedes, real_path = self._handle_file_arg(
/Users/alessandro.lollo/.pyenv/versions/3.9.10/envs/prefect-metricflow/lib/python3.9/site-packages/pyfakefs/fake_filesystem.py:5912: in _handle_file_arg
    wrapper = self.filesystem.get_open_file(filedes)
/Users/alessandro.lollo/.pyenv/versions/3.9.10/envs/prefect-metricflow/lib/python3.9/site-packages/pyfakefs/fake_filesystem.py:1552: in get_open_file
    self.raise_os_error(errno.EBADF, str(file_des))
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

self = <pyfakefs.fake_filesystem.FakeFilesystem object at 0x10fe72eb0>, err_no = 9, filename = '11', winerror = None

    def raise_os_error(self, err_no: int,
                       filename: Optional[AnyString] = None,
                       winerror: Optional[int] = None) -> NoReturn:
        """Raises OSError.
        The error message is constructed from the given error code and shall
        start with the error string issued in the real system.
        Note: this is not true under Windows if winerror is given - in this
        case a localized message specific to winerror will be shown in the
        real file system.
    
        Args:
            err_no: A numeric error code from the C variable errno.
            filename: The name of the affected file, if any.
            winerror: Windows only - the specific Windows error code.
        """
        message = os.strerror(err_no) + ' in the fake filesystem'
        if (winerror is not None and sys.platform == 'win32' and
                self.is_windows_fs):
            raise OSError(err_no, message, filename, winerror)
>       raise OSError(err_no, message, filename)
E       OSError: [Errno 9] Bad file descriptor in the fake filesystem: '11'

/Users/alessandro.lollo/.pyenv/versions/3.9.10/envs/prefect-metricflow/lib/python3.9/site-packages/pyfakefs/fake_filesystem.py:1122: OSError
==================================================== short test summary info ====================================================
FAILED tests/test_example.py::test_example - OSError: [Errno 9] Bad file descriptor in the fake filesystem: '11'
================================================= 1 failed, 8 warnings in 9.07s =================================================

My environment is Python 3.9.10 on MacOS 12.4

Anyone that can help me understanding what’s going on?

Thanks! 🙌