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gh-99029: Fix handling of PureWindowsPath('C:\<blah>').relative_to('C:') #99031

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brettcannon merged 5 commits into from
Nov 25, 2022
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gh-99029: Fix handling of PureWindowsPath('C:\<blah>').relative_to('C:') #99031

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bdfcc65
gh-99029: Fix handling of `PureWindowsPath('C:\<blah>').relative_to('…
barneygale Nov 2, 2022
4b190a1
Restore deleted assertions
barneygale Nov 3, 2022
4d13ac8
Stop using `os.path.relpath()`
barneygale Nov 12, 2022
3b37a0d
Simplify algorithm a little
barneygale Nov 12, 2022
a3e5517
Use f-strings for exception messages
barneygale Nov 19, 2022
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gh-99029: Fix handling of `PureWindowsPath('C:\<blah>').relative_to('… 
…C:')`

`relative_to()` now treats naked drive paths as relative. This brings its
behaviour in line with other parts of pathlib, and with `ntpath.relpath()`,
and so allows us to factor out the pathlib-specific implementation.
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@barneygale
barneygale committed Nov 2, 2022
commit bdfcc65abcb582c79681fb9c9c5c282f4f20fa64
57 changes: 12 additions & 45 deletions Lib/pathlib.py
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Original file line number Diff line number Diff line change
Expand Up @@ -634,57 +634,24 @@ def relative_to(self, *other, walk_up=False):
The *walk_up* parameter controls whether `..` may be used to resolve
the path.
"""
# For the purpose of this method, drive and root are considered
# separate parts, i.e.:
# Path('c:/').relative_to('c:') gives Path('/')
# Path('c:/').relative_to('/') raise ValueError
if not other:
raise TypeError("need at least one argument")
parts = self._parts
drv = self._drv
root = self._root
if root:
abs_parts = [drv, root] + parts[1:]
else:
abs_parts = parts
other_drv, other_root, other_parts = self._parse_args(other)
if other_root:
other_abs_parts = [other_drv, other_root] + other_parts[1:]
else:
other_abs_parts = other_parts
num_parts = len(other_abs_parts)
casefold = self._flavour.casefold_parts
num_common_parts = 0
for part, other_part in zip(casefold(abs_parts), casefold(other_abs_parts)):
if part != other_part:
break
num_common_parts += 1
if walk_up:
failure = root != other_root
if drv or other_drv:
failure = casefold([drv]) != casefold([other_drv]) or (failure and num_parts > 1)
error_message = "{!r} is not on the same drive as {!r}"
up_parts = (num_parts-num_common_parts)*['..']
else:
failure = (root or drv) if num_parts == 0 else num_common_parts != num_parts
error_message = "{!r} is not in the subpath of {!r}"
up_parts = []
error_message += " OR one path is relative and the other is absolute."
if failure:
formatted = self._format_parsed_parts(other_drv, other_root, other_parts)
raise ValueError(error_message.format(str(self), str(formatted)))
path_parts = up_parts + abs_parts[num_common_parts:]
new_root = root if num_common_parts == 1 else ''
return self._from_parsed_parts('', new_root, path_parts)
path_cls = type(self)
other = path_cls(*other)
if path_cls(self.anchor) != path_cls(other.anchor):
raise ValueError("{!r} and {!r} have different anchors".format(str(self), str(other)))
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result = path_cls(self._flavour.pathmod.relpath(self, other))
if result.parts[:1] == ('..',) and not walk_up:
raise ValueError("{!r} is not in the subpath of {!r}".format(str(self), str(other)))
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return result

def is_relative_to(self, *other):
"""Return True if the path is relative to another path or False.
"""
try:
self.relative_to(*other)
return True
except ValueError:
return False
if not other:
raise TypeError("need at least one argument")
other = type(self)(*other)
return other == self or other in self.parents

@property
def parts(self):
Expand Down
12 changes: 3 additions & 9 deletions Lib/test/test_pathlib.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1183,21 +1183,13 @@ def test_relative_to(self):
self.assertRaises(ValueError, p.relative_to, P('/Foo'), walk_up=True)
self.assertRaises(ValueError, p.relative_to, P('C:/Foo'), walk_up=True)
p = P('C:/Foo/Bar')
self.assertEqual(p.relative_to(P('c:')), P('/Foo/Bar'))
self.assertEqual(p.relative_to('c:'), P('/Foo/Bar'))
self.assertEqual(str(p.relative_to(P('c:'))), '\\Foo\\Bar')
self.assertEqual(str(p.relative_to('c:')), '\\Foo\\Bar')
self.assertEqual(p.relative_to(P('c:/')), P('Foo/Bar'))
self.assertEqual(p.relative_to('c:/'), P('Foo/Bar'))
self.assertEqual(p.relative_to(P('c:/foO')), P('Bar'))
self.assertEqual(p.relative_to('c:/foO'), P('Bar'))
self.assertEqual(p.relative_to('c:/foO/'), P('Bar'))
self.assertEqual(p.relative_to(P('c:/foO/baR')), P())
self.assertEqual(p.relative_to('c:/foO/baR'), P())
self.assertEqual(p.relative_to(P('c:'), walk_up=True), P('/Foo/Bar'))
self.assertEqual(p.relative_to('c:', walk_up=True), P('/Foo/Bar'))
self.assertEqual(str(p.relative_to(P('c:'), walk_up=True)), '\\Foo\\Bar')
self.assertEqual(str(p.relative_to('c:', walk_up=True)), '\\Foo\\Bar')
self.assertEqual(p.relative_to(P('c:/'), walk_up=True), P('Foo/Bar'))
self.assertEqual(p.relative_to('c:/', walk_up=True), P('Foo/Bar'))
self.assertEqual(p.relative_to(P('c:/foO'), walk_up=True), P('Bar'))
Expand All @@ -1209,6 +1201,7 @@ def test_relative_to(self):
self.assertEqual(p.relative_to('C:/Foo/Bar/Baz', walk_up=True), P('..'))
self.assertEqual(p.relative_to('C:/Foo/Baz', walk_up=True), P('../Bar'))
# Unrelated paths.
self.assertRaises(ValueError, p.relative_to, P('c:'))
self.assertRaises(ValueError, p.relative_to, P('C:/Baz'))
self.assertRaises(ValueError, p.relative_to, P('C:/Foo/Bar/Baz'))
self.assertRaises(ValueError, p.relative_to, P('C:/Foo/Baz'))
Expand All @@ -1218,6 +1211,7 @@ def test_relative_to(self):
self.assertRaises(ValueError, p.relative_to, P('/'))
self.assertRaises(ValueError, p.relative_to, P('/Foo'))
self.assertRaises(ValueError, p.relative_to, P('//C/Foo'))
self.assertRaises(ValueError, p.relative_to, P('c:'), walk_up=True)
self.assertRaises(ValueError, p.relative_to, P('C:Foo'), walk_up=True)
self.assertRaises(ValueError, p.relative_to, P('d:'), walk_up=True)
self.assertRaises(ValueError, p.relative_to, P('d:/'), walk_up=True)
Expand Down Expand Up @@ -1275,13 +1269,13 @@ def test_is_relative_to(self):
self.assertFalse(p.is_relative_to(P('C:Foo/Bar/Baz')))
self.assertFalse(p.is_relative_to(P('C:Foo/Baz')))
p = P('C:/Foo/Bar')
self.assertTrue(p.is_relative_to('c:'))
self.assertTrue(p.is_relative_to(P('c:/')))
self.assertTrue(p.is_relative_to(P('c:/foO')))
self.assertTrue(p.is_relative_to('c:/foO/'))
self.assertTrue(p.is_relative_to(P('c:/foO/baR')))
self.assertTrue(p.is_relative_to('c:/foO/baR'))
# Unrelated paths.
self.assertFalse(p.is_relative_to('c:'))
self.assertFalse(p.is_relative_to(P('C:/Baz')))
self.assertFalse(p.is_relative_to(P('C:/Foo/Bar/Baz')))
self.assertFalse(p.is_relative_to(P('C:/Foo/Baz')))
Expand Down
3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Library/2022-11-02-23-47-07.gh-issue-99029.7uCiIB.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
:meth:`pathlib.PurePath.relative_to()` now treats naked Windows drive paths
as relative. This brings its behaviour in line with other parts of pathlib,
and with :func:`os.path.relpath()`.