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bpo-40358: add strict parameter to pathlib.PurePath.relative_to #19807

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bpo-40358: add strict parameter to pathlib.PurePath.relative_to #19807

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b3daa47
add tests for pathlib.PurePath.relative_to(strict=False)
domragusa Apr 29, 2020
9892f8b
add strict option for pathlib.PurePath.relative_to
domragusa Apr 29, 2020
3c10a8c
documentation for PurePath.relative_to strict parameter
domragusa Apr 30, 2020
f1fb0a2
add missing news entry
domragusa Apr 30, 2020
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22 changes: 19 additions & 3 deletions Doc/library/pathlib.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -536,7 +536,7 @@ Pure paths provide the following methods and properties:
True


.. method:: PurePath.relative_to(*other)
.. method:: PurePath.relative_to(*other, strict=True)

Compute a version of this path relative to the path represented by
*other*. If it's impossible, ValueError is raised::
Expand All @@ -549,9 +549,25 @@ Pure paths provide the following methods and properties:
>>> p.relative_to('/usr')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "pathlib.py", line 694, in relative_to
.format(str(self), str(formatted)))
File "pathlib.py", line 940, in relative_to
raise ValueError(error_message.format(str(self), str(formatted)))
ValueError: '/etc/passwd' does not start with '/usr'
>>> p.relative_to('/usr', strict=False)
PurePosixPath('../etc/passwd')
>>> p.relative_to('foo', strict=False)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "pathlib.py", line 940, in relative_to
raise ValueError(error_message.format(str(self), str(formatted)))
ValueError: '/etc/passwd' is not related to 'foo'

If the path doesn't start with *other* and *strict* is ``True``,
:exc:`ValueError` is raised. If *strict* is ``False`` and the paths are
not both relative or both absolute :exc:`ValueError` is raised (on Windows
both paths must reference the same drive as well).

.. versionadded:: 3.9
The *strict* parameter was added.


.. method:: PurePath.with_name(name)
Expand Down
28 changes: 21 additions & 7 deletions Lib/pathlib.py
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Expand Up @@ -895,10 +895,10 @@ def with_suffix(self, suffix):
return self._from_parsed_parts(self._drv, self._root,
self._parts[:-1] + [name])

def relative_to(self, *other):
def relative_to(self, *other, strict=True):
"""Return the relative path to another path identified by the passed
arguments. If the operation is not possible (because this is not
a subpath of the other path), raise ValueError.
related to the other path), raise ValueError.
"""
# For the purpose of this method, drive and root are considered
# separate parts, i.e.:
Expand All @@ -920,12 +920,26 @@ def relative_to(self, *other):
to_abs_parts = to_parts
n = len(to_abs_parts)
cf = self._flavour.casefold_parts
if (root or drv) if n == 0 else cf(abs_parts[:n]) != cf(to_abs_parts):
common = 0
for p, tp in zip(cf(abs_parts), cf(to_abs_parts)):
if p != tp:
break
common += 1
if strict:
failure = (root or drv) if n == 0 else common != n
error_message = "{!r} does not start with {!r}"
up_parts = []
else:
failure = root != to_root
if drv or to_drv:
failure = cf([drv]) != cf([to_drv]) or (failure and n > 1)
error_message = "{!r} is not related to {!r}"
up_parts = (n-common)*['..']
if failure:
formatted = self._format_parsed_parts(to_drv, to_root, to_parts)
raise ValueError("{!r} does not start with {!r}"
.format(str(self), str(formatted)))
return self._from_parsed_parts('', root if n == 1 else '',
abs_parts[n:])
raise ValueError(error_message.format(str(self), str(formatted)))
return self._from_parsed_parts('', root if common == 1 else '',
up_parts+abs_parts[common:])

def is_relative_to(self, *other):
"""Return True if the path is relative to another path or False.
Expand Down
82 changes: 82 additions & 0 deletions Lib/test/test_pathlib.py
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Expand Up @@ -613,13 +613,29 @@ def test_relative_to_common(self):
self.assertEqual(p.relative_to('a/'), P('b'))
self.assertEqual(p.relative_to(P('a/b')), P())
self.assertEqual(p.relative_to('a/b'), P())
self.assertEqual(p.relative_to(P(), strict=False), P('a/b'))
self.assertEqual(p.relative_to('', strict=False), P('a/b'))
self.assertEqual(p.relative_to(P('a'), strict=False), P('b'))
self.assertEqual(p.relative_to('a', strict=False), P('b'))
self.assertEqual(p.relative_to('a/', strict=False), P('b'))
self.assertEqual(p.relative_to(P('a/b'), strict=False), P())
self.assertEqual(p.relative_to('a/b', strict=False), P())
self.assertEqual(p.relative_to(P('a/c'), strict=False), P('../b'))
self.assertEqual(p.relative_to('a/c', strict=False), P('../b'))
self.assertEqual(p.relative_to(P('a/b/c'), strict=False), P('..'))
self.assertEqual(p.relative_to('a/b/c', strict=False), P('..'))
self.assertEqual(p.relative_to(P('c'), strict=False), P('../a/b'))
self.assertEqual(p.relative_to('c', strict=False), P('../a/b'))
# With several args.
self.assertEqual(p.relative_to('a', 'b'), P())
self.assertEqual(p.relative_to('a', 'b', strict=False), P())
# Unrelated paths.
self.assertRaises(ValueError, p.relative_to, P('c'))
self.assertRaises(ValueError, p.relative_to, P('a/b/c'))
self.assertRaises(ValueError, p.relative_to, P('a/c'))
self.assertRaises(ValueError, p.relative_to, P('/a'))
self.assertRaises(ValueError, p.relative_to, P('/'), strict=False)
self.assertRaises(ValueError, p.relative_to, P('/a'), strict=False)
p = P('/a/b')
self.assertEqual(p.relative_to(P('/')), P('a/b'))
self.assertEqual(p.relative_to('/'), P('a/b'))
Expand All @@ -628,13 +644,28 @@ def test_relative_to_common(self):
self.assertEqual(p.relative_to('/a/'), P('b'))
self.assertEqual(p.relative_to(P('/a/b')), P())
self.assertEqual(p.relative_to('/a/b'), P())
self.assertEqual(p.relative_to(P('/'), strict=False), P('a/b'))
self.assertEqual(p.relative_to('/', strict=False), P('a/b'))
self.assertEqual(p.relative_to(P('/a'), strict=False), P('b'))
self.assertEqual(p.relative_to('/a', strict=False), P('b'))
self.assertEqual(p.relative_to('/a/', strict=False), P('b'))
self.assertEqual(p.relative_to(P('/a/b'), strict=False), P())
self.assertEqual(p.relative_to('/a/b', strict=False), P())
self.assertEqual(p.relative_to(P('/a/c'), strict=False), P('../b'))
self.assertEqual(p.relative_to('/a/c', strict=False), P('../b'))
self.assertEqual(p.relative_to(P('/a/b/c'), strict=False), P('..'))
self.assertEqual(p.relative_to('/a/b/c', strict=False), P('..'))
self.assertEqual(p.relative_to(P('/c'), strict=False), P('../a/b'))
self.assertEqual(p.relative_to('/c', strict=False), P('../a/b'))
# Unrelated paths.
self.assertRaises(ValueError, p.relative_to, P('/c'))
self.assertRaises(ValueError, p.relative_to, P('/a/b/c'))
self.assertRaises(ValueError, p.relative_to, P('/a/c'))
self.assertRaises(ValueError, p.relative_to, P())
self.assertRaises(ValueError, p.relative_to, '')
self.assertRaises(ValueError, p.relative_to, P('a'))
self.assertRaises(ValueError, p.relative_to, P(''), strict=False)
self.assertRaises(ValueError, p.relative_to, P('a'), strict=False)

def test_is_relative_to_common(self):
P = self.cls
Expand Down Expand Up @@ -1079,6 +1110,16 @@ def test_relative_to(self):
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:'), strict=False), P('Foo/Bar'))
self.assertEqual(p.relative_to('c:', strict=False), P('Foo/Bar'))
self.assertEqual(p.relative_to(P('c:foO'), strict=False), P('Bar'))
self.assertEqual(p.relative_to('c:foO', strict=False), P('Bar'))
self.assertEqual(p.relative_to('c:foO/', strict=False), P('Bar'))
self.assertEqual(p.relative_to(P('c:foO/baR'), strict=False), P())
self.assertEqual(p.relative_to('c:foO/baR', strict=False), P())
self.assertEqual(p.relative_to(P('C:Foo/Bar/Baz'), strict=False), P('..'))
self.assertEqual(p.relative_to(P('C:Foo/Baz'), strict=False), P('../Bar'))
self.assertEqual(p.relative_to(P('C:Baz/Bar'), strict=False), P('../../Foo/Bar'))
# Unrelated paths.
self.assertRaises(ValueError, p.relative_to, P())
self.assertRaises(ValueError, p.relative_to, '')
Expand All @@ -1089,6 +1130,13 @@ def test_relative_to(self):
self.assertRaises(ValueError, p.relative_to, P('C:/Foo'))
self.assertRaises(ValueError, p.relative_to, P('C:Foo/Bar/Baz'))
self.assertRaises(ValueError, p.relative_to, P('C:Foo/Baz'))
self.assertRaises(ValueError, p.relative_to, P(), strict=False)
self.assertRaises(ValueError, p.relative_to, '', strict=False)
self.assertRaises(ValueError, p.relative_to, P('d:'), strict=False)
self.assertRaises(ValueError, p.relative_to, P('/'), strict=False)
self.assertRaises(ValueError, p.relative_to, P('Foo'), strict=False)
self.assertRaises(ValueError, p.relative_to, P('/Foo'), strict=False)
self.assertRaises(ValueError, p.relative_to, P('C:/Foo'), strict=False)
p = P('C:/Foo/Bar')
self.assertEqual(p.relative_to(P('c:')), P('/Foo/Bar'))
self.assertEqual(p.relative_to('c:'), P('/Foo/Bar'))
Expand All @@ -1101,6 +1149,20 @@ def test_relative_to(self):
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:'), strict=False), P('/Foo/Bar'))
self.assertEqual(p.relative_to('c:', strict=False), P('/Foo/Bar'))
self.assertEqual(str(p.relative_to(P('c:'), strict=False)), '\\Foo\\Bar')
self.assertEqual(str(p.relative_to('c:', strict=False)), '\\Foo\\Bar')
self.assertEqual(p.relative_to(P('c:/'), strict=False), P('Foo/Bar'))
self.assertEqual(p.relative_to('c:/', strict=False), P('Foo/Bar'))
self.assertEqual(p.relative_to(P('c:/foO'), strict=False), P('Bar'))
self.assertEqual(p.relative_to('c:/foO', strict=False), P('Bar'))
self.assertEqual(p.relative_to('c:/foO/', strict=False), P('Bar'))
self.assertEqual(p.relative_to(P('c:/foO/baR'), strict=False), P())
self.assertEqual(p.relative_to('c:/foO/baR', strict=False), P())
self.assertEqual(p.relative_to('C:/Baz', strict=False), P('../Foo/Bar'))
self.assertEqual(p.relative_to('C:/Foo/Bar/Baz', strict=False), P('..'))
self.assertEqual(p.relative_to('C:/Foo/Baz', strict=False), P('../Bar'))
# Unrelated paths.
self.assertRaises(ValueError, p.relative_to, P('C:/Baz'))
self.assertRaises(ValueError, p.relative_to, P('C:/Foo/Bar/Baz'))
Expand All @@ -1111,6 +1173,12 @@ 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:Foo'), strict=False)
self.assertRaises(ValueError, p.relative_to, P('d:'), strict=False)
self.assertRaises(ValueError, p.relative_to, P('d:/'), strict=False)
self.assertRaises(ValueError, p.relative_to, P('/'), strict=False)
self.assertRaises(ValueError, p.relative_to, P('/Foo'), strict=False)
self.assertRaises(ValueError, p.relative_to, P('//C/Foo'), strict=False)
# UNC paths.
p = P('//Server/Share/Foo/Bar')
self.assertEqual(p.relative_to(P('//sErver/sHare')), P('Foo/Bar'))
Expand All @@ -1121,11 +1189,25 @@ def test_relative_to(self):
self.assertEqual(p.relative_to('//sErver/sHare/Foo/'), P('Bar'))
self.assertEqual(p.relative_to(P('//sErver/sHare/Foo/Bar')), P())
self.assertEqual(p.relative_to('//sErver/sHare/Foo/Bar'), P())
self.assertEqual(p.relative_to(P('//sErver/sHare'), strict=False), P('Foo/Bar'))
self.assertEqual(p.relative_to('//sErver/sHare', strict=False), P('Foo/Bar'))
self.assertEqual(p.relative_to('//sErver/sHare/', strict=False), P('Foo/Bar'))
self.assertEqual(p.relative_to(P('//sErver/sHare/Foo'), strict=False), P('Bar'))
self.assertEqual(p.relative_to('//sErver/sHare/Foo', strict=False), P('Bar'))
self.assertEqual(p.relative_to('//sErver/sHare/Foo/', strict=False), P('Bar'))
self.assertEqual(p.relative_to(P('//sErver/sHare/Foo/Bar'), strict=False), P())
self.assertEqual(p.relative_to('//sErver/sHare/Foo/Bar', strict=False), P())
self.assertEqual(p.relative_to(P('//sErver/sHare/bar'), strict=False), P('../Foo/Bar'))
self.assertEqual(p.relative_to('//sErver/sHare/bar', strict=False), P('../Foo/Bar'))
# Unrelated paths.
self.assertRaises(ValueError, p.relative_to, P('/Server/Share/Foo'))
self.assertRaises(ValueError, p.relative_to, P('c:/Server/Share/Foo'))
self.assertRaises(ValueError, p.relative_to, P('//z/Share/Foo'))
self.assertRaises(ValueError, p.relative_to, P('//Server/z/Foo'))
self.assertRaises(ValueError, p.relative_to, P('/Server/Share/Foo'), strict=False)
self.assertRaises(ValueError, p.relative_to, P('c:/Server/Share/Foo'), strict=False)
self.assertRaises(ValueError, p.relative_to, P('//z/Share/Foo'), strict=False)
self.assertRaises(ValueError, p.relative_to, P('//Server/z/Foo'), strict=False)

def test_is_relative_to(self):
P = self.cls
Expand Down
2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Library/2020-04-30-02-15-08.bpo-40358.A4ygqe.rst
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@@ -0,0 +1,2 @@
Add strict parameter in :meth:`pathlib.PurePath.relative_to`. Patch by
Domenico Ragusa.