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GH-113528: Deoptimise pathlib._abc.PurePathBase.relative_to() (again) (#113882)

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Restore full battle-tested implementations of `PurePath.[is_]relative_to()`. These were recently split up in 3375dfe and a15a773.

In `PurePathBase`, add entirely new implementations based on `_stack`, which itself calls `pathmod.split()` repeatedly to disassemble a path. These new implementations preserve features like trailing slashes where possible, while still observing that a `..` segment cannot be added to traverse an empty or `.` segment in *walk_up* mode. They do not rely on `parents` nor `__eq__()`, nor do they spin up temporary path objects.

Unfortunately calling `pathmod.relpath()` isn't an option, as it calls `abspath()` and in turn `os.getcwd()`, which is impure.
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Barney Gale 2024-01-09 23:04:14 +00:00 • committed by GitHub
parent 5c7bd0e398
commit cdca0ce0ad
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2 changed files with 42 additions and 15 deletions
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22
Lib/pathlib/__init__.py
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@ -11,6 +11,7 @@ import os
import posixpath
import sys
import warnings
from itertools import chain
from _collections_abc import Sequence
try:
@ -254,10 +255,19 @@ class PurePath(_abc.PurePathBase):
"scheduled for removal in Python 3.14")
warnings.warn(msg, DeprecationWarning, stacklevel=2)
other = self.with_segments(other, *_deprecated)
path = _abc.PurePathBase.relative_to(self, other, walk_up=walk_up)
path._drv = path._root = ''
path._tail_cached = path._raw_paths.copy()
return path
elif not isinstance(other, PurePath):
other = self.with_segments(other)
for step, path in enumerate(chain([other], other.parents)):
if path == self or path in self.parents:
break
elif not walk_up:
raise ValueError(f"{str(self)!r} is not in the subpath of {str(other)!r}")
elif path.name == '..':
raise ValueError(f"'..' segment in {str(other)!r} cannot be walked")
else:
raise ValueError(f"{str(self)!r} and {str(other)!r} have different anchors")
parts = ['..'] * step + self._tail[len(path._tail):]
return self._from_parsed_parts('', '', parts)
def is_relative_to(self, other, /, *_deprecated):
"""Return True if the path is relative to another path or False.
@ -268,7 +278,9 @@ class PurePath(_abc.PurePathBase):
"scheduled for removal in Python 3.14")
warnings.warn(msg, DeprecationWarning, stacklevel=2)
other = self.with_segments(other, *_deprecated)
return _abc.PurePathBase.is_relative_to(self, other)
elif not isinstance(other, PurePath):
other = self.with_segments(other)
return other == self or other in self.parents
def as_uri(self):
"""Return the path as a URI."""