Actual file system change when using pathlib.Path.open() rather than open(pathlib.Path)

[scaramallion]

Describe the bug
I'm getting an actual file system change when using pyfakefs to modify an existing file using pathlib.Path.open() rather than open(pathlib.Path).

How To Reproduce

from pathlib import Path

p = Path(__file__).parent / "foo.bin"
with open(p, "wb") as f:
    f.write(b"\x00\x01\x02\x03")

def test_pffs_open(fs):
    fs.add_real_file(p, read_only=False)
    # Next test passes with open(p, "wb") instead
    with p.open("wb") as f:
        f.write(b"\xDE\xAD\xBE\xEF")

def test_actual():
    with p.open("rb") as f:
        assert f.read() == b"\x00\x01\x02\x03"

Your environment
Please run the following in the environment where the problem happened and
paste the output.

Linux-6.8.0-60-generic-x86_64-with-glibc2.39
Python 3.10.18 (main, Jun  4 2025, 08:56:00) [GCC 13.3.0]
pyfakefs 5.8.0
pytest 8.4.0

[mrbean-bremen]

Thanks - this is actually a known problem.
Though it should only happen up to Python 3.10 - did you see this also for newer Python versions?

[mrbean-bremen]

The workaround is to only use the path string, not the path object in the test (or use open instead of Path.open, which does the same).

[scaramallion]

Thanks - this is actually a known problem.

Ah, fair enough. Thanks