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GH-106037: Disarm os.PathLike foot-shotgun in pathlib.PurePath user subclasses - #106043
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…os.PathLike` We made it possible to subclass `pathlib.PurePath` in a68e585, which landed in 3.12. However, user subclasses automatically inherit an `__fspath__()` method, which may not be appropriate. For example, a user subclass may implement a "virtual" filesystem to provide access to a `.zip` file or FTP server. But it would be highly surprising if `open(FTPPath(...))` attempted to open a *local* file. This patch makes the `os.PathLike` interface opt-in. In pathlib itself, we opt into the `os.PathLike` interface for `PurePosixPath`, `PureWindowsPath` and `Path`. As `PurePath` is not instantiable (you always get a `PurePosixPath` or `PureWindowsPath` object back), this is backwards compatible with 3.11, but not with earlier 3.12 betas.
AlexWaygood
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Jun 23, 2023
AlexWaygood
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Nice idea. Are we sure it's backwards compatible to remove __fspath__ from PurePath? Looks like there are a few user subclasses of it in the wild: https://github.com/pytest-dev/pyfakefs/blob/b576d65bbd9a7508c90e6b00aa3b9eccf4a86fa1/pyfakefs/fake_pathlib.py#L796-L805
One possible alternative solution might be to implement #106046, and then just document that users should set __fspath__ to None if they don't want their path subclasses to be considered subtypes of os.PathLike...?
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We made it possible to subclass
pathlib.PurePathin a68e585, which landed in 3.12. However, user subclasses automatically inherit an__fspath__()method, which may not be appropriate. For example, a user subclass may implement a "virtual" filesystem to provide access to a.zipfile or FTP server. But it would be highly surprising ifopen(FTPPath(...))attempted to open a local file.This patch makes the
os.PathLikeinterface opt-in forpathlib.PurePathsubclasses. In pathlib itself, we opt into theos.PathLikeinterface forPurePosixPath,PureWindowsPathandPath. AsPurePathis not instantiable (you always get aPurePosixPathorPureWindowsPathobject back), this is backwards compatible with 3.11.pathlib.PurePathareos.PathLike#106037